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 Panopæa).

|| 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 Panopea 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.t

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.

* Terquem (1); Terquem (2).

+ Zittel (5), p. 125.

The anterior ribs are narrower and perhaps rather more prominent than the posterior ribs. Delicate and fairly regular lines of growth cross the surface of ribs and interspaces alike. The surface of the shell, where well preserved, is seen to be covered by very numerous and delicate, radially disposed lines of minute granules.

Dimensions. The anterior part of the specimen is hidden in the matrix, but to judge from the course taken by the anterior growthlines, the length of the valve may be fairly accurately estimated as 22 mm. The umbo is situated at about one-third of the total length from the anterior extremity, assuming that the above length-measurement is correct. The height of the valve at the umbonal region is 13 mm. The height of the siphonal border is 8 mm.

Occurrence.-Collected by Mr. Rogers from the highest beds in the kloof behind Colchester, Sunday's River Valley (489g).

Remarks. This is the first specimen of Goniomya recorded from the Uitenhage Series. The condition of the single valve available for comparison scarcely justifies a specific determination, and the question of relationships cannot be usefully discussed without better material for study but the specimen probably represents a new species.

It is interesting to find the genus Goniomya represented here, in strata which yield the peculiar Trigonia of the group of T. vau which so strongly simulate the genus Goniomya both in the arrangement of the costate ornaments and in the general habit. Though the specimen above described at once recalls these Trigonia, it may be readily distinguished from them by the very thin shell-wall and the presence of surface granulation, as well as by the details of ornamentation. In Trigonia vau Sharpe and its allies, the neanic stage is ornamented by concentric ribs passing across the flank and area, and the inclination of the ribs with resulting angular pattern is not produced until the early adult stage. In this Goniomya, the costa formed an anterior and a posterior series, steeply inclined, already in the neanic stage, at a very much shorter distance from the umbonal apex than in the Trigoniæ mentioned.

GENUS THRACIA W. E. Leach.

THRACIA SP.

Plate VIII., fig. 5.

A single specimen, which must be ascribed to this genus, is scarcely so well preserved or so strongly characterised as to allow

of a thorough comparison with known forms, or to warrant the use of a new specific name. The posterior end is slightly broken away so that the exact outline of the shell here cannot be clearly seen. The length is considerably greater than the height; the valves are of a compressed form, most convex in the uppermost third, more flattened below. The umbones are little conspicuous and are directed very slightly backwardly; they are situated just posteriorly to the middle of the shell. The upper margin slopes down very gently in front of the umbo, with an almost straight profile which passes into the evenly convex outline of the frontal margin. The posterior compressed area is well defined, especially in the neighbourhood of the umbo.

Occurrence. In the railway cutting between milestones 24-243 on the line between Uitenhage and Graaff-Reinet, about three miles from Uitenhage (331).

Remarks. Comparison with English specimens of Thracia phillipsi Roem., from the Speeton Clay, shows that these differ widely from the shell before us by their much more inflated and prominent umbonal region and more steeply sloping antero-superior margin. In general form and outline the African shell shows close similarity to Thracia subtruncata Meek, from the Cretaceous strata of Sucia Islands (British Columbia).t The outline also somewhat nearly resembles that of Thracia gracilis Meek and Hayden, from Cretaceous sandstone at the mouth of the Judith River (on the Missouri), but the latter is rather more elongated posteriorly.

Another shell which may be brought into close comparison occurs in the Aptian of Spain (Obon and Utrillas) and was described by Coquand § as Periploma lorieri. To judge by Coquand's figure, this differs from the Uitenhage form by the steeper inclination of the carinal ridge and the more nearly parallel direction of the upper and lower margins anteriorly to the umbo.

Mya depressa Phillips, (1), Tab. 2, fig. 8 (non Sow.); Thracia phillipsi F. A. Roemer, (2), p. 74, Taf. 10, fig. 1 (1841).

Whiteaves (2), p. 140, pl. 17, fig. 7.
Meek (2), p. 224, pl. 39, fig. 6.

§ Coquand (1), p. 100, pl. ix., figs. 5, 6.

Thracia robinaldina (d'Orbigny) is distinguished by its more oblong and less ovate outline, and its more conspicuous umbones. The African shell compares again more closely with the figure of a specimen from the Lower Cretaceous (Rolling Downs Formation) of Queensland, ascribed by Etheridge with some doubt to Thracia primula Hudleston, and figured under the generic name Corimya.+ Less similarity is shown to the specimen originally named Thracia primula, preserved in the British Museum (Natural History); this has greater relative height anteriorly to the umbo, a more curved inferior margin, more strongly compressed valves, a less inflated umbonal region, and less definitely developed posterior carination.

GENUS GASTROCHENA L. Spengler.

GASTROCHENA DOMINICALIS Sharpe.

1856. Gastrochæana dominicalis D. Sharpe, Trans. Geol. Soc. Lond., ser. 2, vol. vii., p. 198, pl. xxiii., fig. 4.

Sharpe described under this name a shell which had bored into a fragment of wood, found on the Sunday's River "near Enon." He also mentions the occurrence of Gastrochana boring into fragments of wood and Trigonia-shell, also from the Sunday's River.

Fragments of fossil wood bored by Gastrochana were collected by Messrs. Rogers and Schwarz from an oyster bed at the base of the cliff below the old school-house at Dunbrodie, Sunday's River (336). The shells are concealed within the short calcareous tubes which line their cavities, and some of these crypts measure about 6 mm. in length. There is no reason to doubt that these specimens represent the same form as that described by Sharpe. This shell was also found boring into lignite in strata of the "Wood Bed" series of the Bezuidenhout's River below Blue Cliff station.

66

§ Sharpe spoke of this fragment as bone," but this was corrected on p. 228 of Sharpe's paper and by Prof. T. Rupert Jones in an editorial footnote to Tate's paper in 1867, Tate (1), p. 155.