42 



of ventral margin li lines ; the anterior ventral angle is about J of a line 

 more remote from the umbones than the posterior angle. 



None of the specimens examined are quite perfect, and it seems pro- 

 bable that in some the posterior wing may be proportionally a little larger. 

 In the one figured, a piece apj&ars to have been broken off. 



D. D. Owen has figured a small species, under the name of Pleurorhyn- 

 chus antiqua, in his Report on the Geology of Wisconsin and Iowa, PL 2 

 B. Fig. 19. His figure shows the body of the shell and the anterior wing, 

 but not the posterior siphonal wing. Judging from so much as is exhibited, 

 the ventral margin of the body of the shell does not project so far below 

 the lowerjmargin of the anterior wing as it does in this species. Owen 

 found his specimen in the Lower Silurian rocks at Lower Fort Garry, on 

 the Red River, in the Hudson Bay Company's territory. 



It may be. s that this species belongs to an undescribed genus, but until 

 the interior can be seen, we are compelled to place it in ' Conocardium on 

 account of its external characters. 



Locality and Formation. Paquette Rapids, on the Ottawa Eiver. 

 Black River limestone. 



Collectors. Sir W. E. Logan, E. Billings. 



MODIOLOPSIS MBYERI. (N. sp.) 



Fig. 44. 

 Fig. 44. Modiolopsis Meyeri. 



Description. Transversely sub-ovate, alated posteriorly, rather strongly 

 ventricose. The umbones are a little flattened and the beaks strongly in- 

 curved. From the umbones a strong oblique gibbosity extends diagonally 

 downwards and backwards, becoming obsolete near the lower posterior angle. 

 The hinge line is straight and about half the whole transverse length of 

 the shell. The posterior half of the dorsal margin is elevated into a rather 

 prominent rounded alation, thence descending with an uniform gentle curve 

 to the posterior extremity, which is narrowly rounded and confined to the 

 lower half of the shell. Ventral margin gently convex ; anterior extre- 

 mity small, about one-seventh" the whole transverse length. 



