GASTEROPODA. 10 3 



calcareous shales on the shore of Lake Erie at Eighteen-mile creek. It is not 

 rare in the form of casts near Cumberland, Md. It occurs in the limestone 

 above the hydraulic beds at the Falls of the Ohio.* 



Bellerophon rudis. 



PLATE XXIV, FIGS. 13, 14, 15. 



Bellerophon rudis, Hall. Descriptions of New Species of Fossils, etc., p. 29. 1861. 

 " " Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 57. 1862. 



" " " Illustrations of Devonian Fossils : Gasteropoda, pi. 23. 1876. 



Shell extremely ventricose, the inner volutions rounded and subglobose ; 

 umbilicus small ; the last half of the body-volution abruptly expanded, 

 and the peristome spreading almost rectangularly to the axis of the shell. 

 Anterior margin of the peristome slightly sinuous, and spreading on the 

 posterior side over the preceding volution. The upper part of the last 

 volution is marked by strong transverse arching costae, which are closely 

 arranged on the summit of the volutions, but towards the aperture, become 

 irregular, stronger and more distant : the expanded portion of the volution 

 has two, three or more strong folds or wrinkles parallel to the margin of 

 the peristome, which are stronger in the middle, and become obsolete on 

 each side : the upper part and sides of the volution are marked by lon- 

 gitudinal ridges which reach nearly to the margin in front, but in some 

 parts are irregular and obscure ; this feature is subject to great variation, 

 being in some specimens scarcely perceptible. 



This shell resembles in form the B.patulus, but is more robust, and the trans- 

 verse costae fewer and stronger; the concentric folds on the expanded portion, 

 as well as the longitudinal ridges on the sides, are distinguishing characters. 

 In one specimen the transverse diameter is about one inch and seven-eighths, 

 ami the longitudinal diameter nearly one inch and three-fourths. The 

 general proportions are so nearly like B. patulus that it might perhaps be 



* For information regarding the ajre of tbifl limestone at the Falls of the Ohio, heretofore referred to the 

 Upper Helderberg group, see note at the end of descriptions of the Gasteropoda. 



