MOLLUSCA. 545 



front of the umbonal ridge is a more or less obscure depression 

 or broad shallow sinus, which passes obliquely backward from the 

 beak to the sinuosity in the ventral margin. The postero-dorsal 

 slope concave to the cardinal margin, where the surface is 

 inflected to form the escutcheon. In front of the beak the surface 

 of the shell is inflected to form the rather large lunule. In the 

 casts the muscular impressions are of moderate size, inconspic- 

 uous or somewhat strongly marked, and the free margins are not 

 crenate. Surface of the shell marked by concentric lines of 

 growth which vary in the strength of their development. 



Remarks. This specific form seems to have been described 

 under several names by different authors, Conrad's name trape- 

 zoidea having priority. The types of the species Venilia trape- 

 zoidea, Crassatella monmouthensis and Veniella subovalis have 

 all been carefully studied in the collection of the Philadelphia 

 Academy of Science. The specimens indicated as types of C 

 'monmouthensis are four in number; the smallest of these has 

 "type" marked on it in ink, and seems to be different from the 

 other three; it has the shell preserved, and from its lithologic 

 character seems to have come from one of the marl beds, probably 

 the Navesink; this smaller specimen is apparently not the one 

 which was illustrated by Gabb. The three larger individuals 

 agree with the original illustration of the species in all essential 

 characters, and one of them was doubtless used as the original for 

 the figure; these specimens apparently came from the Merchant- 

 ville formation, and are identical with V. trapezoidea and with 

 the Merchantville clay specimens in the recent collections of the 

 Survey. Whitfield's Veniella subovalis is certainly a member of 

 the same species, although its posterior margin is somewhat 

 higher and more nearly vertical than the others. The type of 

 Crassatella lineata has not been seen, but the species is represented 

 in the National Museum at Washington by numerous examples 

 from the type locality, and it is unquestionably specifically 

 identical with the Alabama and New Jersey specimens. An 

 examination of a large number of individuals of this species shows 

 considerable variation in some respects, notably in the height of 

 the posterior truncated margin, and in the curvature of the basal 



35 PAI, 



