530 Systematic Paleontology 



Cucullwa vulgaris Morton, 1834, Synop. Org. Rem. Cret. Group, U. S„ p. 64, 



pi. iii, fig. 8; pi. xiii, fig. 5. 

 Cucullwa capax Conrad, 1858, Jour. Acad. Nat. Sci., Phila., 2d ser., vol iii, 



p. 328, pi. xxxv, fig. 2. 

 Cucullwa tippana Conrad, 1858, Ibidem, p. 328. 



Cuculhca vulgaris Gabb, 1862, Proc. Acad. Nat. Sci., Phila for 1861, p. 326. 

 Cucullwa vulgaris Meek, 1864, Check List Invert. Fossils N. A., Cret. and 



Jur., p. 8. 

 Cucullwa tippana Meek, 1864, Ibidem. 



Idonearca vulgaris Cook, 186S, Geol. of New Jersey, p. 376, text figure. 

 Iclonearca vulgaris Conrad, 1868, Ibidem, p. 725. 



Idonearca vulgaris Gabb, 1876, Proc. Acad. Nat. Sci., Phila., p. 313. 

 Idonearca tippana Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 95, pi. 



xii, figs. 19-21. 

 Idonearca vulgaris Whitfield, 1885, Ibidem, p. 98, pi. xiii, figs. 1-5. 

 Idonearca medians Whitfield, 1885, Ibidem, p. 199, pi. xxvi, figs. 5, 6. 

 Cucullwa vulgaris Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 8. 

 Cucullwa tippana Johnson, 1905, Ibidem. 

 Cucullwa vulgaris Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 



p. 397, pi. xxxii, figs. 5, 6. 

 Cucullwa tippana Weller, 1907, Ibidem, p. 394, pi. xxxi, figs. 5-10; pi. xxxii, 



figs. 1, 2. 



Description. — " Ventricose, triangular, flattened before ; beak promi- 

 nent and incurved ; shell thick, with numerous delicate longitudinal stria?. 



" Length an inch and a quarter ; breadth an inch and three-fourths." — 

 Morton, 1830. 



Type Locality. — Chesapeake and Delaware Canal, Delaware. 



Shell very thick and heavy, moderately large, evenly inflated, the young 

 sub-quadrate in outline, the adults obliquely produced along the posterior 

 keel ; anterior margin squarely truncate dorsally, merging ventrally with 

 a broad and gentle curve into the basal margin, which is approximately 

 horizontal in the young, but becomes increasingly oblique as the form 

 matures; posterior lateral margin squarely truncate in the young forms, 

 obliquely truncate in the adults ; umbones very prominent, distant, ortho- 

 gyrate, their summits somewhat flattened ; external surface sculptured 

 with exceedingly fine radial lira;, crowded but rather irregular in spacing, 

 tending, however, to be arranged in pairs, often less feeble upon the 

 posterior keel, though more distant and occasionally obsolete upon the 

 flattened posterior area ; radial sculpture relatively strong in the umbonal 



