82 Annals of the South African Museum. 



" Ostrea aquilina" by Coquand,* closely resembles many specimens 

 of E. imbricata in the form and inflation of the valves and in the 

 degree of curvature of the umbonal region ; but it differs by the 

 more marked carination of the larger valve. Eemes has considered 

 both the Chilian shell and Exogyra imbricata Krauss to be identical 

 with Sowerby's Exogyra sinuata,} but this is certainly an error. 

 The same author, however, has figured an Exogyra from Stramberg,J 

 ascribed by him to Exogyra subsinuata Leym., to which selected 

 individuals of E. imbricata, in which the surface of attachment is 

 relatively large, may show considerable resemblance. 



An exogyrate shell from the Bajocian of Abyssinia was ascribed by 

 Douville to E. imbricata Krauss, but this was an erroneous identi- 

 fication, as already pointed out by G. Miiller.|| The resemblance 

 of the small specimens figured by Douville to selected young 

 individuals of E. imbricata is indeed not a distant one, but many 

 of the Uitenhage specimens are attached by a very much larger 

 surface, and, moreover, attain a colossal size in comparison with 

 Douville's types, if these represent the adult stage. The variation 

 in E. imbricata is so great that a more detailed and critical com- 

 parison could not be entered upon without a substantial suite of 

 specimens of the Abyssinian shell. 



A shell from the Isakondry basin in Madagascar (presumably 

 from strata of Lower Cretaceous age) is stated by Douvill6 to bear 

 a close resemblance to Exogyra imbricata Krauss. II 



GENUS MYTILUS Linnaeus. 

 MYTILUS UITENHAGENSIS sp. nov. 



Plate II., figs. 10, 11, lla. 



Description. The shell is slender and elongated in outline, sharply 

 pointed in front, and antero-ventrally truncated. The hinge-margin 

 is straight, and passes backwardly by a curve into the obliquely 

 sloping posterior margin, which is only very slightly convex in 

 outline until the posterior end of the valve is reached. In profile, 

 the antero- ventral margin is straight, passing from the acutely 

 pointed umbo to the posterior angle of the valve, where it abruptly 

 cuts the curved outline of the posterior margin. 



The antero-ventral area is flat, and its surface is perpendicular 



* Coquand (2), p. 158. f Eemes (1), p. 216. 



J Kernes (1), pi. xxi. (iv.), tigs. 2a, 26. 



Douvilte (1), p. 230, pi. xii., figs. 8, 9. || G. Muller (1), pp. 569, 570. 



IT Douvilte (2), p. 388; Douville (4), p. 215; Lemoine (1), p. 176. 



