INVERTEBRATE PALEONTOLOGY. 153 



obliquely and strongly incurved, in young shells located near the anterior 

 side, though nol quite as prominent as the margin below, but in the adult 

 sometimes overhanging the anterior margin; lunule excavated, but apparently 

 nol defined by a marginal ridge; posterior umbonal ridge very prominenl 

 and strongly angular from the beaks to the posterior basal angle, while the 

 space between it and the dorsal margin is concave; surface showing con- 

 centric stria 1 , and generally a few stronger ridges. 



Length of the largest specimen seen, 1.G0 inches; height of same, 1.38 

 inches: convexity, 1.55 inches. 



('asts of this species show the posterior lateral teeth of the hinge to 

 present the usual character's of the genus; while in one specimen, the poste- 

 rior cardinal tooth of the right valve can he seen to be strong and deeply 

 bifid. Another specimen shows the middle cardinal tooth of the left valve 

 to be strong, prominent, broadly trigonoid conical, and slightly curved upward 

 at the end, as in the type-species, and the posterior cardinal to be narrow 

 and arcuate; the oblique, trigonal pit for the middle cardinal tooth of the 

 other valve, occupying the space between the two. None of the specimens 

 show the anterior cardinal tooth of either valve; but enough of the hinge 

 and other characters can be determined to remove all doubt in regard to its 

 being a true typical Veniella, and not a Venilicardia. 



Generally, the internal casts of this species retain no traces of the 

 surface-markings, but sometimes they present faint remains of concentric 

 undulations. The posterior umbonal ridges, however, are always strongly 

 defined, and angular even on internal casts. Some large specimens have, in 

 casts, a strong, obtuse ridge near the dorsal margin of each valve, apparently 

 bounding a kind of broad-lanceolate escutcheon, the middle and deeper part 

 of which is occupied by the rather narrow ligament. 



Young specimens of this shell present much the general outline of small 

 individuals of Veniella (Venilicardia) obtruncata, Stoliczka (Palseont. Ind., Ill, 

 pi viii, fi<zs. 7 and 7, a, b) ; but they have the umbonal ridge of each valve 

 much more sharply defined, while the hinge-characters of the two shells 

 are altogether different. Of course, if Dr. Morton's name Venilia should be 

 retained for this genus, the name of this species would become Venilia 

 goniopkora. 



Locality and position. — Missouri Rivei-, near Fort Benton ; Fort Benton 

 group of the Cretaceous. 

 20 H 



