1G0 • PALAEONTOLOGY OF ILLINOIS. 



allous, should be regarded as belonging to a distinct section from the type of 

 that genus. 



Locality and position : Same as last. Also in the Chouteau limestone of 

 Moniteau and other adjoining counties of Missouri, and in the same position 

 in th is State. 



Genus BELLEROPHON, Montfort, 1810. 



(Conch. Syst., ii, p. 174.) 



Bellerophon cyrtolites, Hall. 



PI. 14, Fig. 80, 8b. 



Bellerophon cyrtolites, Hall, Dec, 1860. Thirteenth Ann. Report Regents University 

 N.Y., p. 107. 



Shell small, sub-lenticular ; sides converging with a slightly 

 convex outline, from near the umbilicus to the prominent 

 angular periphery ; volutions apparently about two and a half, 

 increasing rather rapidly in size, each of those within, about 

 three-fourths embraced by the succeeding turn, last one becom- 

 ing obtusely angular around the umbilicus; aperture cordate; 

 lips broadly and deeply sinuous at the dorsal angle ; umbilicus 

 (in casts) about one-third the breadth of the outer whorl, deep 

 and conical ; surface of casts retaining obscure traces of marks 

 of growth, which in crossing the sides of the whorls from the 

 umbilicus, make a graceful curve forward, and in approaching 

 the dorsal angle, curve very strongly backwards, so as to indi- 

 cate the presence of a very profound but not sharply denned 

 sinus, in the lip. Greater diameter of a large specimen, 0.66 

 inch; breadth at the aperture, 0.35 inch. 



This species belongs to a section of lenticular species, for which one of the 

 writers has proposed the name Trojridodiscus* with B. curvilineatus, of Conrad, 

 as its type. These shells differ from the type of the genus Bellerophon (j5. 

 vasulites), Montfort, in their lenticular form, often carinated dorsum without a 



* Proceed. Chicago Acad. Sci., Vol. 1, p. 9, March, 18GG. 



