434 Prof. T. Rupert Jones — Carboniferous Shale from Siberia. 



Posidonomya memhranacea, McCoy (Synop. Carb, Foss., p. 78, 

 pi. xiii, fig. 14), is an elongate form with delicate concentric lines; 

 but it is larger, and differs in shape from Fig. 1 ; it also has some 

 longitudinal lines crossing the others. P. lateralis, Sowerby & 

 Phillips, is also one of the obliquely elongate species, but it is much 

 larger, and it has coarse concentric wrinkles. 



No. II (Figs. 6 and 7). — This right valve is evidently allied to 

 the foregoing, but has proportionately less length, a fuller convexity 

 of the postero-inferior margin, and a greater obliquity, at an angle 

 of 40° with the hinge-line. This may probably belong to Anthra- 

 comya Icsvis, Dawson. 



No. Ill (Fig. 5). — This is a left valve, having features similar to 

 those of Figs. 6 and 7, but much more pronounced. The obliquity 

 is 65° instead of 40°. The hinge-line is short, and the postero- 

 inferior margin is elongate - elliptical. The concentric lines are 

 not so neat. This is possibly a variety of A. Icevis, modified by 

 pressure. 



No. IV (Figs. 16, 17). — This left valve has a much more truly 

 rounded inferior margin than that of Fig. 5, and approximates 

 to a semicircle; its obliquity to the hinge-margin is greater (75°). 

 It may be compared with some of the figures of Anthracomya 

 Valenciensis, E. Etheridge, jun., given by Dr. W. Hind (Mon. Pal. 

 Soc, 1895, p. 113, pi. xvi, figs. 44-48). 



No. V. — Figs. 8-15 are subovate Posidonomyce (P. suhovata), having 

 the umbo either more or less excentric or just in the middle of the 

 hinge-line. They have a nearly semicircular inferior margin, and 

 numerous concentric lines, ridgelets, or rugulje. Fig. 10 has the 

 umbo near the middle of the upper margin ; and is very similar in 

 shape to Posidonomya punctatella, Jones, from a Lower Carboniferous 

 shale in Western Scotland. It measures 8 mm. transversely, by 

 6 mm. in height. Many larger valves, found in the same shales, 

 having a similar shape, but with fewer and stronger concentric 

 ridges, have been regarded as adult individuals, measuring 32 x 22, 

 30 X 18, 29 X 22, 28 x 20, 20 x 11, as I was informed by my old 

 friend the late Dr. J. Young, of Glasgow, who sent me many 

 sketches of them, with strong concentric ridges and nearly semi- 

 circular valves. These shales, especially at Dairy in Ayrshire and 

 Thornliebank near Glasgow, bear crowds of Posidonomyce, con- 

 centrically ribbed, oblong-ovate in shape, mostly equilateral, with 

 more or less median umbo and semicircular inferior margin. Among 

 them, at Linn Spout,^ Dairy, and at Arden quarry, Thornliebank, 

 occurred the P. punctatella, Jones,^ once regarded as an EstTieria 

 (1869), but afterwards proved to be a Posidonomya (1890), and it is 



^ For a section of the Fpper Linn limestone and Posidonomya bed of the Lower 

 Carboniferous Series at Linn Spout, see the Mon. Brit. Pal. PhyU., Palaeont. 

 Soc, 1899, pt. iv, p. 208. 



» Trans. Geol. Soc. Glasgow, 1867, vol. ii, p. 71, pi. i, fig. 5 ; 1890, vol. ix, 

 pp. 85-87, pi. V, fig. 7. 



