a much more complex nature. If, in a suitably preserved adult specimen, the surface half-way down the valve and below this be examined under slight magnification and with favourable illumination, it is seen that the raised interspaces or minute flattened ribs. themselves exhibit a peculiar punctate structure on that side of the rib nearest to the lateral margin of the valve. This is developed in such a way that the outer margin of each little rib is cut into by a series of minute wedge-shaped indentations, which leave more prominent projecting portions of the rib standing out somewhat after the manner of the hydrothecæ on a graptolitic stipe. In some cases the successive wedge-shaped grooves may almost cross the rib, but for the most part the margin of the rib which is nearest to the middle line of the valve is straight and entire.

Another peculiarity of the ornamentation is seen in some cases in the manner in which, when the radial striæ are traced upwards from the valve-margin towards the place of convergence at the middle line, by favourable illumination they may be observed to be continued upwards across the middle line, giving rise to a slight intercrossing here.

In the left valve the anterior ear is large and rectangular, the posterior ear small. This valve has a rather more equilateral aspect than the right valve, which is sometimes very markedly inequilateral.

No. (3) is Tate's figured type specimen.

Occurrence.-Railway cutting between milestones 24-24 on the Uitenhage to Graaff-Reinet railway (297, 350); also obtained by Miss M. Wilman at Coega River. Tate says: "Collected by Dr. Rubidge in a soft, yellowish-grey, sandy limestone at the Zwartkop River Heights, and at Prince Alfred's Rest; in both localities it is frequent."

Remarks. The notched sculpture of the ribs, described above, may be well observed when the preservation is exceptionally good. It appears only in faint traces in a portion of the surface of one of the specimens examined by Tate, and in other individuals less well preserved the markings only consist of radiating linear striæ, obscurely punctate in places, with smooth interspaces. A right valve from the Coega River, which agrees closely with Tate's figured type, has the surface so well preserved that the intimate details of sculpture exhibited call for the above additional descriptive note.

The delicate notched structure is also well shown in specimens from the above-mentioned locality near Uitenhage.

Tate brought this shell into relationship with Pecten lens Sowerby, a Jurassic form; and although it shares with this and with the Portlandian P. morini de Loriol* some of the principal features which characterise these familiar Jurassic types, yet it may equally well be brought into comparison with Cretaceous forms. The Jurassic shells mentioned, besides differing in the outline, have simply striæ with a punctate structure, but no encroachment of this sculpture into the interspaces between the linear striæ. Pecten suprajurensis Buvignier, an Upper Jurassic form, approaches much more closely to P. projectus in general character and outline, possessing a similar bulging frontal profile, but is likewise merely ornamented by delicately punctate linear striæ with smooth interspaces, attaining, moreover, much larger dimensions. Pecten buchi Roem., ‡ also Upper Jurassic, is well distinguished by its almost equilateral outline and by the minute transverse striations which cross the interspaces between the radial linear striæ.

Pecten striato-punctatus Roemer,§ from the Neocomian and Aptian of Europe, is more equilateral in outline and is more delicately ornamented; the punctate structure is much more minute and confined wholly to the striæ, leaving the very narrow intervening spaces smooth.||

Pecten curvatus Geinitz, though having greater relative height than P. projectus, sometimes seems to approach the somewhat inequilateral form of this, though in figures of other shells which have been united with P. curvatus** the valves are almost equilateral. Although Geinitz figured the magnified ornamentation of the valvesurface so as to produce an aspect of sculpture widely different from that given for instance by Reuss, yet it appears from the descriptions that punctate linear striæ with smooth interspaces characterise these forms.

Nilsson's P. virgatus, of Upper Chalk age from Sweden, tt is * de Loriol and Pellat (1), p. 107, pl. x., fig. 6. Buvignier (1), p. 24, pl. xix., figs. 21-23.

F. A. Roemer (1), pl. xiii., fig. 8 (1836), and Nachtrag, p. 27; de Loriol, Royer and Tombeck (1), p. 389, pl. xxii., figs. 12, 13.

§ F. A. Roemer (1), Nachtrag, p. 27; d'Orbigny (3), p. 592, pl. 432, figs. 4–7

(1847); Woods (3), vol. i., p. 157, pl. xxix., figs. 4-6 (1902).

|| See also figures given by de Loriol under the name P. arzierensis; Loriol (3), pl. iv., figs. 3-5. Geinitz (1), p. 16, Taf. iii., fig. 13.

** Geinitz (2), Theil i., p. 193, Taf. 43, fig. 15 (1872); Theil ii., Taf. 10, fig. 1, (1872); Reuss (1), part ii., p. 28, Taf. 39, fig. 6 (as P. divaricatus).

tt Nilsson (1), p. 22, Tab. ix., fig. 15.

more equilateral and more coarsely ornamented than P. projectus, and it has been shown, moreover, by Hennig that Nilsson's unsatisfactory figure is misleading; this shell really has relatively strong ribs with linear interspaces, increasing by division and insertion and not diverging from the middle line in the manner represented by Nilsson. The delicate transverse striæ which cross the radial ornaments are scarcely comparable with the notching of the "ribs" shown by P. projectus. The shell from the Gosau beds described by Zittel under the name P. virgatust is almost equilateral, and is much higher in outline than P. projectus.

The shell from the Cretaceous of the east end of Maud Island (Queen Charlotte Islands), ascribed to Camptonectes curvatus Geinitz by Whiteaves, is somewhat similar to P. projectus, to judge from the figure of a right valve, but it is more equilateral in form.

A Pecten from the Neocomian in German East Africa was described by G. Müller § under the name P. striato-punctatus, but the specimen figured is so preserved that a comparison with P. projectus is difficult, although it appears to differ from this in being more equilateral.

Pecten (Camptonectes) pueyrrydonensis Stanton, || from the Belgrano beds (Lower Cretaceous) of Patagonia is another shell of similar type, but differs at least in the more equilateral form of the right valve.

Pecten kamerunensis von Koenen,¶ from Lower Cretaceous strata in the Cameroons, differs from P. projectus by the more equilateral form and the rather coarser ornamentation, with stronger lateral ribdevelopment. Von Koenen describes how the furrows appear here and there divided by swellings into little grooves, but says that this stands in connection with the crossing of lines of growth-a relation not to be observed in the minute ornamentation of P. projectus.

SUB-GENUS CHLAMYS J. F. Bolten.

PECTEN (CHLAMYS) cf. SUBACUTUS Lamarck.

Plate II., figs. 6, 6a.

Cf. 1819. Pecten subacutus J. B. de Lamarck, Hist. Nat. des Anim.

*

sans Vert., vol. vi., p. 181.

Hennig (1), p. 41, pl. 2, figs. 28, 33.
Whiteaves (3), p. 242, pl. 32, fig. 4.

Zittel (2), p. 109, pl. xvii., fig. 8. § G. Müller (1), p. 550, Taf. 24, fig. 7.

|| Stanton (3), p. 12, pl. iv., fig. 1.

¶ von Koenen (1), p. 20, Taf. iii., figs. 14, 15.

Cf. 1847. Pecten subacutus A. d'Orbigny, Paléont. Franç., Terr. Crét.,

vol. iii., p. 605, pl. 435, figs. 5-10.

1872. Pecten subacutus H. B. Geinitz, Das Elbthalgeb. in Sachsen, part i., p. 195, pl. xliv., fig. 5 (Palæontographica, vol. xx.).

1902. Pecten (Chlamys) subacutus H. Woods, Mon. Cret. Lamell. Engl., vol. i., part iv., p. 169, pl. xxxi., figs. 7-9.

(Palæontographical Society.)

Descriptive Note.-A single specimen sent from the collection of the South African Museum seems to approach very closely to P. subacutus. The shell is ovate in outline, prolonged dorsally, with an acute apical angle (about 80°). The inflation is slight, with the left. valve a little more convex than the right.

The valves are ornamented by about 22 strong, angular ribs with sharp summits. Near the inferior margin the summits of the ribs are separated from one another by a distance of about 2 mm. On parts of the shell the ribs are studded with numerous blunt, spinose projections. Where the surface is well preserved the ribs and interspaces are seen to be ornamented by very delicate, transverse linear markings, most clearly visible in the interspaces. Near the inferior margin these become obscurely developed and are masked by coarser ridges and grooves of accretion. The hinge-line and ears are unfortunately not preserved, but having regard to the other characters there is no reason to suppose that they differed essentially from those of P. subacutus.

Dimensions.-Height (about) 42 mm.; length 35 mm.

Occurrence.-Marine Beds of Sunday's River (304).

Remarks.-Pecten subacutus is characteristic of the Cenomanian in Europe, but this African shell approaches more closely to it than to any form from the Lower Cretaceous with which I am acquainted. In the imperfect material at disposal, no features are apparent which would justify a definite separation from the European form, yet in the absence of the ears in this specimen and the lack of further comparative material, the question of identity must remain open.

Pecten urgonensis de Loriol,* common in the Urgonian of Grand Salève, is a shell of very similar type, so far as can be judged from de Loriol's description and figures; but apparently its scaly ornaments are larger and more prominent, and the surface is perhaps more coarsely ribbed.

* de Loriol (2), p. 389, pl. C, figs. 25, 26.

GENUS LIMA J. G. Bruguière.
SUB-GENUS ACESTA H. and A. Adams.

LIMA (ACESTA) OBLIQUISSIMA Tate.
Plate II., fig. 7.

1867. Lima obliquissima R. Tate, Quart. Journ. Geol. Soc., vol. xxiii., p. 156, pl. ix., fig. 5.

Supplementary Descriptive Note. The shell has great height in comparison with length. The posterior outline is gently rounded, the anterior profile straight. The straight anterior border passes at its lower end by a somewhat sudden curve into the rounded inferior border. The valves are most convex in the umbonal half and near the anterior side; they become flatter posteriorly and inferiorly. Anteriorly, the flank passes abruptly, though without marked carination, into an extensive, flat frontal face, truncating the shell. This frontal area is in no degree sunk or concave in form. The umbones are acute and sharp, terminal at the anterior extremity of the hinge-line; the superior border of the shell is straight and very short, and truncates the shell to form a right angle with the anterior border. The anterior ear is rudimentary or not developed; the posterior ear is much reduced, and not definitely demarcated from the flank.

The ornamentation consists of delicate linear radial grooves, very crowded near the umbo, gradually diverging until, at a distance of 40 mm. from the umbo, they may be separated by interspaces 2 mm. broad. At a distance exceeding 30 mm. from the umbo, these lines are almost or quite absent from the middle part of the flank, though well impressed on the lateral parts. The lines follow a more or less irregular and wavy course and are sometimes suddenly deflected to right or left when traced down from a prominent concentric growth-line. When well preserved, the linear ornaments show a minutely punctate structure, most perfectly developed in the umbonal half of an adult shell. The interspaces are very gently convex or are flat, but are without sculpture. On the frontal area the ornaments are of a more pronounced character, and may take the form of imbricating ridges with the edges directed away from the valve-margin. They radiate from the umbonal region and pass along the frontal face, gradually approaching the frontal valve-margin and forming an acute angle with this. On the frontal. area, therefore, the ornaments are very obliquely crossed by the lines of accretion.