198 CARBONIFEROUS LAMELLIBRANCHIATA. 



however, differs in the following points from N. attenuata. The anterior end is 

 comparatively shorter, the inferior border more curved. The umbones are more 

 elevated, more acute and non-contiguous, and the escutcheon is much excavated, thus 

 forming a narrow ridge on its outer border. It would appear that the Liassic 

 form is intermediate in shape between N. attenuata, Fleming, and N. stilla, M'Coy. 



M'Coy seems to have been of the opinion that Phillips's reference to Sowerby's 

 species was erroneous ; for in his remarks on A T . clavata he says, " This species 



is easily distinguishable from N. attenuata, Fleming ; in general 



appearance it comes nearest to N. claviformis, Sowerby, but that is a Lias 

 species," &c. 



I have doubtfully placed the N. birostrata, M'Coy, as a synonym of N. 

 attenuata ; but the original specimen of the former seems to have disappeared, and 

 the shell now labelled with that name in the Griffith Collection of the Science 

 and Art Museum, Dublin, is that of a species quite different from the original 

 figure. N. leiorhynchus, M'Coy, is probably the young of the species under discus- 

 sion ; it has exactly the form of the young shells of N. attenuata, found with full- 

 grown examples in the Scottish localities. Of these I have depicted a series, 

 PL XV, figs. 12—15. 



The original of N. leiorhynchus, M'Coy, is shown in PL XV, fig. 16, and is 

 evidently a young shell. 



M'Coy's description of N. leiorhynchus is " transversely ovate, width rather 

 more than twice the length, convex. Posterior [anterior] end rounded, gibbose ; 

 anterior end [posterior] produced into a long narrow beak, rounded at the point ; 

 surface marked with strong, regular, equal, transverse striae, which disappear as 

 they reach the anterior [posterior] end, leaving the long beak-like anterior 

 [posterior] extremity smooth." 



The original shell was not very perfect, and the typical large escutcheon is 

 not seen, therefore it cannot be stated with absolute certainty whether it is the 

 young form of N. attenuata or of N. Sharmani, R. Etheridge, jun. 



The descriptions of N. clavata and N. longirostris, M'Coy, do not in any way 

 correspond with the figures; and I am of opinion that the references to the 

 figures were accidentally transposed in each case, and that the figure of 

 N. clavata is described as N. longirostris, and vice versa. I have therefore 

 given the description of N. clavata and the figure of N. longirostris in the 

 synonyms of N. attenuata. The other shell is, I consider, a synonym of N. 

 Isevirostrum, Portlock, so that fortunately no question of nomenclature will arise. 



The original specimen from which the figure of N. longirostris was drawn 

 seems to have disappeared, and a very poor example is on the tablet bearing 

 that name in the Griffith Collection in the Science and Art Museum, Dublin. 

 The original description is meagre, and does not mention the escutcheon : 



