72 



[Senate 



IFiG. 4. The interior of the ventral valve, showing foramen, area, etc. enlarged. 



Fig. 5. Interior of the dorsal valve enlarged, showing the foveal plates, dental sockets, and the 



quadripartite muscular impression ; the valve slightly distorted. 

 Fig. 6. A similarly enlarged dorsal valve, showing some variations from the preceding. 



Geological relations. The lowest position- in which this genus is known is in 

 the Marcellus shale, where we have a single species. There are three species in the 

 Hamilton group, one in the Chemung group, and one in the Coal measures. 



GENUS VITULINA ( n. g.) . 

 [ Lat. Vitula, a goddess.] 

 Generic description. Shell planoconvex, semielliptical, marked by four or five 

 simple rounded plications on either side of the mesial fold and sinus. Ventral 

 valve very convex, gibbous in old specimens; the mesial fold consisting of two 

 larger plications, with a shallow depression between them. Dorsal valve de- 

 pressed convex or nearly flat, with a defined mesial sinus, in the bottom of 

 which there is a flattened or slightly elevated fold. Area large, confined to the 

 ventral valve; its length occupying two-thirds the length of the cardinal line, 

 and sometimes nearly the entire length. Foramen very large, broadly triangular, 

 reaching to the apex of the ventral valve, and its base half the length of the area* 

 The cardinal processes and foveal plates of the dorsal valve are conspicuous in 

 the foramen. Surface minutely pustulose; the pustules arranged in radiating 

 lines, those of each line alternating with those of the next. 

 The interior of the ventral valve has the dental lamellae well developed, and ter- 

 minating at the lower angles of the foramen in strong somewhat rounded dental 

 processes. Within the foramen, at the apex of the shell, a strong callosity extends 

 across the rostral cavity, but does not reach to the exterior margins. From this 

 callosity, a slender mesial septum extends half way to the base of the shell : on 

 each side of this are the muscular impressions. The interior of the dorsal valve 

 shows the cardinal process extending in a low rounded mesial septum which 

 reaches below the middle of the shell, each side marked by a distinct groove. 

 The foveal plates are narrow and very divergent. 



This genus possesses characters somewhat intermediate to Tropidoleptfs and 

 Leptocgelia, when we consider the general form of the shell, but differs from both 

 in internal structure. The strong dental lamellae and dental processes extend from 

 the lower angles of the area; while in Tropidoleptus, the teeth are oblique, 

 crenulate, and distinctly separate from the area. 



Fig. 1. Exterior of the dorsal valve, showing 

 the pustulose surface : enlarged. 



Fig. 2. Interior of the ventral valve, enlarged : 

 tt, teeth ; 00, the thickened dental 

 lamellae. 



