243 



Width of an average specimen 24 lines ; height 15 lines : width of 

 umbilicus 11 lines ; width of last whorl 9 lines. 



This species differs from M. crenulata in being of a more rotund form, 

 the outer edge of the body whorl obtusely rounded, the umbihcus wider, 

 and the edge not crenulated. 



M. transitionis may be only a variety. 



Locality and Formation.— I, K, L, M, N, Point Rich and Table 

 Head, Newfoundland ; Quebec group. 



Collector. — J. Richardson. 



OTHER SPECIES OF MACLUREA. 



a 



Fig. 228. 



Fig. 229. 



Figs. 228, 229, 230. — Opercula of different species oi Maclurea. 



At Cape Norman, associated with M. oceana, the three forms of opercu- 

 lum above figured were found, evidently belonging to distinct species. 

 The one represented by fig. 229, occurs abundantly and in a fine state of 

 preservation. The outer surface is divided into two sub-triangular areas 

 by a suture running from the nuclear angle a, to the lower inner angle. 

 The inner or smaller area is striated parallel to the inner concave edge b ; 

 the outer area parallel to the lower gently convex edge c. It is about 

 two Hnes in thickness at the lower edge, but becomes gradually thicker to 

 the upper, the most elevated point being at the nuclear angle, a, where 

 the thickness is ten lines in the specimen figured. On the inside, the 

 upper and outer edges are bordered by a thick elevated margin. There 

 is no muscular process, as there is in the operculum found with M. 

 crenulata. 



