16 



vated, thread-like radiating lines, which on the posterior 

 part of the shell are crossed by finer concentric striae, giv- 

 ing that part of the shell a cancellated appearance. Ante- 

 rior depressed end marked by much fainter radiating lines 

 crossed by nearly obsolete traces of fine striae, which con- 

 verge towards the anterior tubular wing. 



Length, '20 to *33 of an inch. 



Locality. — Alton, 111. 



Conocardium equilaterale. — Shell triangular, sub-equi- 

 lateral, scarcely gibbons in the middle ; hinge line very 

 straight ; beaks small, rising a little above the hinge line ; 

 anterior end cuneate, sloping gradually from near the centre 

 of the shell ; umbonial ridge obtuse above, nearly at right 

 angles to the hinge, and sub-dividing several times before 

 reaching the base ; posterior end cuneate, very gradually 

 sloping from the body of the shell ; extremity unknown. 

 Surface marked by radiating stria) or folds, which are simple 

 or bifurcating, and crossed by fine, regular, elevated, thread- 

 like lines. 



Length and width nearly equal, about *125 of an inch. 

 Locality. — Spergen Hill, la. 



NUCULA, Lamarck. 



v Nucula Shumardana. — Shell obliquely ovate or sub-cune- 

 ate, gibbous towards the beaks ; beaks anterior, elevated, ap- 

 proximate or in contact ; anterior end vertically truncate ; 

 posterior side cuneate, sloping from the beak ; cardinal line 

 forming an angle of about 80° at the beak ; base forming a 

 broad curve from the anterior and posterior cardinal mar- 

 gins. Surface marked by regular equidistant, sub-imbrica- 

 ting striae, rarely with unequal concentric folds. Hinge line 

 somewhat strongly crenulate ; ligamentary pit distinct, 

 triangular. 



Length, *09 to '21, width -08 to '17 of an inch. 

 Locality. — Spergen Hill ; Bloomington. 



