T. C. Brown — Fauna from Ckappaquiddich Island. 231 



Modiola vineyardensis sp. n. PI. I, fig. 1. 



Shell strongly ventricose, with a very prominent, almost 

 angular nmbonal ridge extending from the beak to the ventral 

 margin. Shell distinctly concave anterior to this ridge ; pos- 

 terior to this ridge it becomes flattened toward the posterior 

 margin ; anterior end extremely short barely extending beyond 

 the beak ; posterior margin angulate, front margin nearly 

 straight only a slight emargination occurring, basal end 

 rounded ; the portion of the margin from the end of the hinge 

 line to near the point of angulation, and from beyond the point 

 of angulation to the ventral margin, are almost straight lines. 

 Surface with pronounced raised radii, flattened at the top and 

 separated by spaces equal to or slightly wider than the radii ; 

 the radii are very fine and crowded on the anterior portion of 

 the shell, much coarser on the median and posterior region, 

 and distinct from the beak to the margin. They increase in 

 size progressively from the dorsal to the ventral portion of the 

 shell, with a corresponding increase in the width of the inter- 

 spaces. They increase in number by intercalation as well as 

 bifurcation. Fine distinct growth lines cross and cancellate 

 the radii. 



This species resembles M. alahamensis Aldrich,* from the 

 Eocene of Maryland, but differs from it in general outline. It 

 has a less curved anterior border and more radii, which are very 

 distinct from the margin to the beak. The shell is shorter 

 antero-posteriorly, and the posterior margin is more obtusely 

 angulate. The shell of M. vineyardensis is also more ventri- 

 cose and the umbonal ridge more angular and more pro- 

 nounced. 



In general outline this species approaches more nearly M. 

 grammatus Dall,f from the Oligocene of Florida. The sur- 

 face ornamentation is very similar, but judging from Ball's 

 figure his shell is less ventricose and the umbonal ridge less 

 angular and less distinct. 



But even closer than to any of these is the resemblance of 

 this species to M. elegans Sowerby^: from the Eocene of Eng- 

 land as figured and described by Wood among the Eocene 

 bivalves. In general outline and surface ornamentation the 

 resemblance is very close. M. elegans is, however, slightly 

 less angulate at the postero-dorsal margin and judging from 

 the figures is less ventricose. 



Compared with the modern M. plicatula Lamarck, living 

 along the Atlantic coast, M. vineyardensis seems to be nar- 



* Bull, of Am. Palaeont., vol. i, p. 68, pi. v, fig. 13. 



f Trans. Wagner Free Institute of Sci., vol. iii, pt. 4, p. 794, pi. xxx, fig. 2. 

 % Paleontological Soc. Monographs, London 1861-71. Eocene Bivalves, 

 p. 65, pi. xii, fig. o (c). 



