GENUS SOLECURTUS H. D. de Blainville.
SOLECURTUS sp.

Text-figure 1.

Description of a Single Specimen.-The specimen is a right valve, slightly imperfect at the siphonal margin. The umbo is very inconspicuous, and is situated slightly in front of the middle of the shell. The upper margin slopes down very gently in front and behind the umbo. The frontal margin is short and has a rounded convex profile; towards this margin the upper and lower valve-borders very gently converge. Towards the siphonal margin the valve has a slightly greater height than in the anterior half. The surface is marked by lines of accretion, but no trace of ornamentation has been observed. The inflation of the valve is very slight.

Occurrence.-Found at Grass Ridge, 3 miles east-north-east of Uitenhage (310).

*

Remarks. The single specimen examined is not quite complete at the posterior end, and, unfortunately, the surface is so preserved as to leave no traces of faint linear sculpture, if such markings were ever present. By following the growth-lines it is possible to arrive at the original form of the posterior border. In shape the shell agrees very closely with Solecurtus warburtoni Forbes, from the Aptian of Atherfield (Isle of Wight); the umbo occupies a similar position, and the valve is anteriorly rounded, with diminished height towards the frontal border, while posteriorly the height is greater. The only clearly observable difference is that, in specimens of similar dimensions, the measurement from the umbo vertically to the inferior margin is relatively rather smaller in the English shell.

* Forbes (1), p. 237, pl. ii., fig. 1.

This also has very faint and delicate radial, linear ornamentation on the anterior part of the flank, but the African shell may originally have borne similar minute sculpture, and on this point nothing further can at present be said.

Similar forms were described by d'Orbigny, under the name Solen, from the Lower Cretaceous (S. robinaldinus)* and from the Chalk (S. æqualis). Guéranger has figured a shell from the Cenomanian of the Sarthe under the name Solecurtus æqualis, to which our specimen appears to bear a close resemblance, so far as comparison is possible.

GENUS MACTRA Linn.

MACTRA? DUBIA sp. nov.

Plate VIII., figs. 2, 2a, 3, 3a.

Description.-The shell has greater length than height, and the umbones are situated at rather more than one-third of the shell's total length from the anterior extremity. The inflation is moderate, and most strong just above the middle of the valves. The umbones are somewhat weakly developed and are not very prominent. The cardinal margin and the posterior margin form together a curved outline which passes down, posteriorly very steeply, to a marked angular junction with the lower border. From the umbo a wellmarked carina passes obliquely across the posterior part of the valve, down to the postero-inferior angle of the valve-margin. The carina marks off a flattened or very slightly concave postero-superior area which occupies less than one-quarter of the total valve-surface. In front of the umbo the valve-margin slopes down to form a somewhat sharply curved outline in front, the foremost point of the anterior margin falling well within the lower half of the shell. The long pallial margin shows a broadly convex outline, sometimes slightly flattened towards the posterior end. The greatest height of the valve occurs at the umbonal part. The surface is smooth, with numerous delicate growth-lines, and shows closely spaced radial rows of very minute punctæ, only visible under a lens.

Occurrence.-Found in the cliff on Buck Kraal, Sunday's River

(141h).

Remarks.-The doubtful reference of this form to Mactra is, it must be admitted, unsatisfactory. The generic position, in fact, is very uncertain, for the characters of the hinge are unknown and the ligament space is relatively extensive. The general aspect of the shell does not accord well with either Cyprina or Meretrix. The specimens share with Mactra angulata J. de C. Sow. (Blackdown Beds), the sub-angular junction of the posterior and inferior margins and the presence of a defined ridge running obliquely from the umbo down to the base of the posterior margin. In M. angulata, however, the shell is more triangular and less ovate in outline, and the umbonal region is more prominent and tumid, less anteriorly placed, and less strongly directed forwards.

Mactra warrenana Meek and Hayden (Cretaceous of Dakota) † is in some degree comparable, but differs by its more trigonal form, more prominent umbonal region, and the presence of a defined lunule of relatively large size.

GENUS PLEUROMYA L. Agassiz.

PLEUROMYA BAINI (Sharpe).

Plate VIII., figs. 4, 4a.

1856. Myacites? bainii D. Sharpe, Trans. Geol. Soc. Lond., ser. 2, vol. vii., p. 195, pl. xxii., fig. 7.

Occurrence. The locality given by Sharpe was merely "Sunday River." Specimens were collected by Messrs. Rogers and Schwarz at Grass Ridge, 3 miles east-north-east of Uitenhage (317, 318, 334, 335), from an outcrop of nodular limestone, the highest fossiliferous outcrop of this locality, where many characteristic fossils of the Sunday's River Beds were found. P. baini was also found to occur commonly in the railway cutting between milestones 241–24 on the line from Uitenhage to Graaff-Reinet. Mr. Rogers obtained a very well-preserved specimen from the highest beds in the kloof behind Colchester, Sunday's River Valley (495g).

Remarks.-There is some variation in the form of the shell, and the inferior margin, though never showing a strongly curved outline, is not always so straight as depicted in Sharpe's figure. When well

J. de C. Sowerby (2), p. 341, pl. xvi., fig. 9.

↑ Meek (2), p. 208, pl. xxx., fig. 7.

Rogers and Schwarz (1), p. 9.

preserved the surface is seen to be covered with closely spaced radial lines of delicate granules.

Although possessing no highly distinctive external features, this shell retains a certain characteristic aspect, while approaching somewhat closely to some European representatives of the genus. It may usually be easily distinguished from the larger Pleuromya lutraria (Krauss),* another characteristic shell of the Sunday's River Beds, with which it is associated. If mature specimens be compared, P. lutraria is distinguished by its much larger dimensions. If small specimens of this be brought into comparison with mature examples of P. baini of equal size, there is a considerable general similarity between them; but P. lutraria, when young, has a definite ornamentation of rounded concentric ribs, whereas P. baini is a smooth shell, with the surface only marked by lines of growth and minute granules. The umbones of P. lutraria are rather more prominent, and are perhaps situated a little nearer to the anterior extremity, while the margin in front of the umbo slopes down more suddenly than in P. baini.

Pleuromya neocomiensis (d'Orb.) † is a similarly elongated form, but is distinguished by marked anterior truncation. P. rostrata (d'Orb.) is more produced posteriorly and has a more curved inferior outline. Some individuals of P. baini closely resemble a Pleuromya from the Lower Greensand of the Isle of Wight which has been considered, apparently erroneously, to represent d'Orbigny's P. neocomiensis, and is much more likely to be identical with P. schröderi (Wollemann), § from the Neocomian of North Germany. To judge from Dr. Wollemann's description and figure, P. schröderi approaches very closely indeed to P. baini.

Another shell which shows considerable resemblance to P. baini occurs in the Neocomian sandstone of the Teutoburger Wald, and was ascribed by Weerth,|| though perhaps erroneously, to d'Orbigny's Panopaa neocomiensis; the general similarity is great, but the shell figured by Weerth has an inferior margin presenting a rather more curved outline.

The shell from the Neocomian of North Germany, described by F. A. Roemer ¶ as Pleuromya solenoides, is an elongated form with

* Krauss (2), p. 447, Tab. xlvii., fig. 1.

† d'Orbigny (3), p. 329, pl. 353, figs. 3–8 (1845).

‡ d'Orbigny (3), p. 333, pl. 355, figs. 3, 4 (1845).

§ Wollemann (1), p. 126, Taf. v., fig. 7 (as Panopœa).

|| Weerth (1), p. 37, Taf. viii., fig. 7.

F. A. Roemer (3), p. 330, pl. xli., figs. 20 21.

straight upper margin and little-curved lower margin. P. baini differs from this in being more equilateral and less produced and truncated posteriorly.

As regards the generic position of this shell, although the hingecharacters have not been described and I have been unable to investigate them, there is no reason to doubt that we are dealing with a typical Pleuromya, to which genus belong also, in all probability, the majority of the Neocomian forms to which the name Panopæa was formerly applied. There is no reason to suppose that the hingecharacters of P. baini differ essentially from those of P. lutraria, with which it is associated; and although it was the nature of the hinge that led Krauss to propose for the latter form the separate generic name Anoplomya, it appears plain from Terquem's detailed studies of the genus Pleuromya that the name proposed by Krauss must be regarded as a synonym-a view already adopted by Zittel.†

GENUS GONIOMYA J. L. R. Agassiz.

GONIOMYA sp.

This genus is represented by a single specimen of a small right valve. It is unfortunately imperfect, with a large part of the shell substance removed, and it is embedded in a very hard matrix which cannot be removed without further injury to the delicate shell.

Description. The valve has little convexity and is posteriorly well produced. The umbo is rather pointed and prominent and shows a weak fold of the valve-surface extending for a short distance on its posterior side. The shell-substance is very thin and delicate. The ribbed ornaments of the surface are developed already close to the umbonal apex, where the anterior and posterior ribs are very delicate and closely spaced and are steeply inclined to form the V-pattern. The angle of the V is very acute, and the successive angles formed by the junction of the ribs of the two series are situated at first just below the umbonal apex, and then below one another on the flank on a slightly oblique line posteriorly inclined, so that the lowest angles of the sculpture are situated more backwardly than those above. The most backwardly situated ribs, which do not contribute to the angular ornamentation, are posteriorly inclined when traced down from their upper terminations. Posteriorly to the umbo there is a broad smooth area devoid of sculpture on the upper part of the valve, but this is not sharply demarcated from the flank.