190 Trans. Acad. Set. of St. Louis. 



Avicula circulus * but his name must be considered as a 

 synonym of Pernopecten cooperensis. The oolite specimens 

 are usually larger than those from the subjacent yellow sand- 

 stone, but are about the same size as those usually found in 

 the Vermicular sandstone fauna at Northview, Missouri. t 



CONOCARDIUM PULCHELLUM W. & W. 



PL XVII. f. 2-3. 



Original description. " Shell small, general form triangu- 

 lar, with ventricose valves. Hinge line straight, the length 

 equal to that of the posterior slope. Anterior end cuneate ; 

 posterior end obliquely truncate. Basal line gently arcuate, 

 widely gaping near the anterior extremity; hiatus elongate 

 ovate, distinctly crenate on the inner border. Beaks minute, 

 incurved, situated posteriorly ; umbonal slope rounded, pos- 

 terior space concave; siphonal tube small. Entire surface 

 marked by distinct, diverging radii, those of the posterior 

 space a trifle finer than those of the body of the shell; also 

 by very fine concentric striae." 



The dimensions of the type specimens are: length along 

 hinge line 7 mm., greatest height 6 mm., thickness of both 

 valves 5 mm. 



Remarks. This little species is strongly suggestive of some 

 of the small species of Conocardium which occur in the 

 Spergen Hill fauna in Indiana at the horizon of the St. Louis 

 limestone. The resemblance is even more striking because 

 of the similarity of the lithologic characters of the beds con- 

 taining the fossils at the two localities, both formations being 

 white oolitic limestone. The Burlington species, however, 

 is distinct from any of those in the Spergen Hill fauna, its 

 greatest resemblance being with C. meekanum. 



GASTEROPODA. 

 Loxonema sp. undet. 



PI. XVII. f. 9. 



The interior casts of a species of Loxonema are not uncom- 

 mon in the oolite bed, but no specimens preserving the shell 



* Rep. Geol. Surv. la. 1 2 :522. The original A. circulus Shuin., is dis- 

 tinct. 



t Trans. Acad. Sci. St. Louis. 9 : 24. 



