l!ASTIJ<>miA. -'-I 



expand. .lin K ' below almo-t to the periphery of the outer volutinn; concave 



on each side of the latter, the inner ed^e thick and with a rounded central swelling 

 which continues inwardly as a rounded ridge; inner aperture subtriangular, the 

 inner or lateral angles rather sharp, the outer more obtuse. Surface marked by 

 -tn.n^r. regular, tliread-like lines of growth, of which, on an average specimen, 



\e to fourteen occur in " inin. The course of the stria- from the umbilicus to 

 the slit-band is gently curved in the central half, but more strongly at each end. 

 Slit-hand very rarely preserved; when perfect it surmounts a low ridge, is of 

 ni< .derate width, concave, bordered on each side by a thin sharp line, and covered 

 !>y more or less unequal lunula*. In casts of the interior the umbilicus is much 

 r. sharply defined and very abrupt, the ventral side of the volutions appearing 

 to he almost Hat and the section of the outer one triangular. 



This fine species is related to B. plafyxdnnn and H. similis, but has a thicker shell 

 than either of the Trenton species. This shows itself especially in the much 

 stronger development of the inner lip, and in the smaller umbilicus. As casts of the 

 interior, in which condition all three of these species are most commonly met with, 

 />'. Hi'thri may l>e distinguished from the others by the impression of the callosity of 

 the inner lip which causes the umbilical cavity to appear as drawn out narrowly 

 above. The volutions besides enlarge more rapidly, and the umbilicus, especially 

 when compared with H. similis, is deeper and much more sharply defined. 



Good testiferous specimens are very rare, many being distorted by pressure, 

 and in most of them the greater part of the aperture is broken away, and the 

 surface markings obscured by weathering or maceration. The majority, however, 

 preserve a large part of the expanded inner lip. 



F<>rmtin* and locality.- Not iin<-<>iiiiiinii in the upper part of th<> Kirlmioml tfrnupnf tin- Cincinnati 

 perlul at Ki<-)i!iiiul. Indiana. We have It also fn>in Lincoln enmity. Ki-nlu 



CMtetimt.-E. O. Ulrlch. 



liK.M.Kllol-IION CAPAX, ft. Sp. (Ulrirll.) 

 PLA1K I. Mil. Hi.S. 50 an.l 51: PLATK LXIV. FIGS. -. 



This species agrees closely with />'. mhri. l>ut on comparison proves to differ in 

 a greater or lesser degree in nearly every feature. First, the volutions enlarge more 

 rapidly, second, they are more ventricose, third, the umbilicus in casts is a trifle 

 smaller and more rounded at the edge, fourth, the outline of the aperture is less 

 narrowly rounded on the sides, and fifth, the cross-section of the outer volution of 

 casts is nearer semicircular than triangular. The shell is larger, the volutions 

 increase in size much faster, the umbilicus is smaller, and the inner lip much heavier 

 than in B. platystotna and H. similis. When the aperture is imperfect, specimens of 



