51 



DisciNA Circe. (N. sp.) 



Pig. 55. Fig. 56. 



Fig. 55. — Discina Circe. JFig. 56.— D. Pelopea. 



Description. — Circular ; lower valve with the apex central or very nearly 

 so ; peduncular groove acutely oval, extending from the apex about two- 

 thirds the distance to the margin. The foramen- is probably situated at 

 the outer extremity of the groove, but it cannot be seen in the specimen 

 examined. The upper valve (supposed to be that of this species,) has the 

 apex situated about one-third the semi-diameter from the marg^. In both 

 valves the apex is smooth. 



Surface with rather strong, sub-lamellose concentric stvigs, which become 

 more distant and coarser from the apex outwards. At the margin there 

 are four or five ridges in 1 line, but next to the apex double that number 

 in the same space. The ridges are somewhat irregular, being in some 

 places slightly undulated, and occasionally branched, two or more running 

 into one. The grooves are rather wider than the ridges, and the lamellose 

 aspect of the latter appears to be due to their beiag more abruptly elevated 

 on the inner side, or the side towards the apex than on the outside. 



Width of the specimen of the lower valve examined, 9 lines ; length of 

 peduncular sulcus, 3i lines ; width of same, i a line. Another specimen 

 (an upper valve) is 7 lines wide. 



The lower valve is depressed, conical, and appears to have been about 

 2 lines in height, but as it is somewhat distorted by pressure, the true 

 elevation cannot be determined. The upper valve seems to be less convex 

 than the lower. 



The species described by Prof. Hall, imder the name of Orbicula lamel- 

 losa, (Pal. N. Y., Vol. 1, p. 99, pi. 30, figs. 10 a J,) appears to be a 

 smaller and more finely striated species. It may be that the figures repre- 

 sent a young individual of this species ; but, at all events, the name pro- 

 posed by Prof. Hall cannot be retained, as it was pre-occupied by another 

 and very distinct species, D. lamellosa. (Brod. Zool. Proc. 1833, p. 124.) 



This species also resembles D. Forlesii (Davidson,) a Wenlock lime- 

 stone species, but differs in having the apex of the lower valve central, 

 instead of eccentric. 



