398 CRETACEOUS PALEONTOLOGY. 



1861. Cucullaca vulgaris Gabb, Synop. Moll. Cret. Form., p. 



174 (118). 

 1864. Cticull&a vulgaris Meek, Check List Inv. Foss. N. A., 



Cret. and Jur., p. 8. 

 1868. Idonearca vulgaris Con., Cook's Geol. N. J., p. 725, p. 



376, figure. 

 1876. Idonearca vulgaris Gabb, Proc. Acad. Nat. Sci. Phil., 



1876, p. 313. 

 1886. Idonearca medians Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 199, pi. 26, figs. 5-6. 

 1905. Cucullaa vulgaris Johns., Proc. Acad. Nat. Sci. Phil., 



1905, p. 8. 



Description. Internal casts subtriangular in outline, subcune- 

 ate behind; the dimensions of a large, nearly perfect specimen, 

 are: length, 40 mm.; height, 32 mm.; thickness, 32 mm. Shell 

 very oblique, the beaks of the internal cast large, widely sepa- 

 rated and greatly elevated above the hinge-line. Anterior mar- 

 gin curving backward and downward from the anterior extremity 

 of the hinge-line into the gently convex basal margin ; postero- 

 basal extremity prominent, sharply rounded or subangular ; pos- 

 terior margin obliquely truncate. Valves with a strong, angular 

 umbonal ridge, becoming especially prominent towards the pos- 

 tero-basal extremity; the postero-dorsal slope abrupt, indented 

 by the deep and strong, crescentiform cavity left by the pos- 

 terior muscular ridge. Anterior muscular impression of moder- 

 ate strength. Pallial line usually strongly defined, especially 

 posteriorly, represented in the casts by an elevated ridge crossed 

 by sharply defined elevated ridges which are short and close 

 anteriorly, becoming -longer, stronger and more distant pos- 

 teriorly, especially where the pallial line crosses the umbonal 

 ridge. 



Remarks. The original examples of this species consist of 

 sixteen specimens in the collection of the Philadelphia Academy 

 of Science, accompanied by Morton's original label, and one of 

 them was undoubtedly the individual used as the original for his 

 figure of the species, although it is not possible to determine 

 which one was actually the type specimen used for illustration 



