INVERTEBRATES. 385 



Genus BELLEROPHON, Montfort, 1808. 



(Conch. Syst., i, p. 50.) 



Bellerophon crassus, M. and W.. 



PL 31, fig. 16 a, 16 6. 



Bellerophon crassus, Meek and Worthen. October, 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 458. 



Shell large, very thick, subglobose, or a little longer than 

 wide; volutions expanding moderately, rounded over the dor- 

 sum and sides; umbilical region somewhat excavated; mesial 

 band narrow, rather prominent, and subangular; aperture 

 transverse, reniform or sublunate; lip strongly thickened near 

 the umbilical excavations on each side, but not covering them, 

 thinner and moderately prominent in outline on each side of 

 the narrow sinus in the outer margin, and spreading in the form 

 of a rather thick, smooth callous, over the inner whorls, and 

 between the callosites on each side ; surface marked by rather 

 distinct striae of growth, and irregular, transverse wrinkles, 

 which latter are strongest in the umbilical region and near the 

 aperture ; lines of growth and wrinkles making a very gentle 

 forward curve in crossing from the umbilicus to the dorsal band. 

 Greatest length, 2.26 inches; breadth, 2 inches; ditto of aper- 

 ture, 1.70 inches; breadth of mesial band near the aperture, 

 about 0.12 inch. 



This fine Bellerophon resembles, somewhat, B. costatus, Sowerby, as figured 

 by de Koninck {Ann. Foss., pi. xxvi, fig. 2), but differs in having its aperture 

 less expanded, its umbilicus more exposed, and its surface not near so regularly 

 and distinctly costated. Its marks of growth are also much less arched back- 

 wards as they approach the mesial band, thus indicating a much smaller sinus 

 in the lip. Our specimen is somewhat weathered, but its marks of growth 

 appear never to have been near so strongly defined on the mesial band, as rep- 

 resented by de Koninck's figures of B. costatus. 



It has more nearly the form of de Koninck's figures of B. vasulites, Montfort, 

 but differs in not being regularly costate, and in having the callosites of its lip 

 less developed in the umbilical region. 



Locality and position: Pittsburg, St. Clair county, 111.; Lower Coal Measures. 



49 Sept. 28, 1SG6. 



