The Invertebrate Fauna of the Uitenhage Scries. 81 



into comparison. The shells figured by Coquand * as Ostrea couloni 

 include narrow forms, more elongated and more decidedly carinated 

 than E. imbricata, as well as a broad type, developing plications 

 of the larger valve in the later adult stage, which is in no respect 

 closely comparable with the form we are considering. 



Sowerby's Exogyra sinuata,\ though itself very variable, is 

 typically widely separated from E. imbricata by the strong carina- 

 tion of the larger valve and the widely expanding form of this, with 

 the much less arcuate habit of growth and the considerably greater 

 adult dimensions. Some French forms figured by Leymerie and 

 brought into relationship with Sowerby's species, though perhaps 

 erroneously, afford, on the other hand, material for a close com- 

 parison with E. imbricata. Thus, Leymerie's E. sinuata, var. 

 elongata J can be fairly closely matched, while extreme individuals 

 of E. imbricata, in their narrow outline and very arcuate growth, 

 nearly resemble that author's figure of E. subsinuata, var. aquilina. 

 The shell from the Neocomian of the Haute-Marne figured by Bayle || 

 as Aetostreon aquilinum (Leym.), again, closely resembles very narrow 

 and curved specimens of the African form. 



Ostrea tardensis Stanton, H from the Lower Cretaceous Gio beds 

 of Patagonia, may, in selected individuals, somewhat closely 

 approach E. imbricata, but its near relationship to this must be 

 considered doubtful ; it seems, however, to represent in some 

 respects an analogous type. The exogyrate character of the 

 umbonal region is only feebly indicated, according to Dr. Stanton, 

 who says that the " lower valve is very thick and very convex, 

 obscurely carinate, with the beak more or less twisted laterally, but 

 not distinctly coiled." It differs also by frequently acquiring a 

 marked crescentic form in the adult. If the Patagonian shell had 

 a true exogyrate ancestry, which appears probable, the early 

 characters seem to have so far disappeared as to indicate that 

 relationship to E. imbricata is probably somewhat remote. 



The shell from the Neocomian of Arqueros in Chili described by 

 Bayle and Coquand as Ostrea couloni, '"''' and afterwards brought into 

 association with a heterogeneous company under the collective name 



* Coquand (2), p. 180, pi. 65, fig. 10 ; pi. 71, figs. 8-10; pi. 74, figs. 1-5; pi. 75, 

 figs. 1-6, 22. 



f J. Sowerby (1), vol. iv., Tab. 336 (1822). [As Gryphaa.] 



I Leymerie (2), p. 17, pi. 12, fig. 2. 



Ibid., pi. 12, figs. 6, 7. 



|| Bayle (1), pi. cxl., figs. 3-5. 



<f Stanton (3), p. 11, pi. i., figs. 1, 2 ; pi. ii., figs. 1, 2. 



* Bayle and Coquand (1), p. 37, pi. vii., figs. 1, 2. 



