PLATE 46. 



Page 



Fig. 1 a- z. Pentamerus galeatus. 257 



1 a, 6, c. Young shells which are free from plications. 



1 d, e,/. Views of a young specimen which has become very gibbous, and with plications 

 strongly developed upoi; the mesial fold. 



1 g, h, i. Three figures of half-grown individuals, showing the different degrees of develop- 

 ment in the plications. 



1 fc, I. Dorsal and front views of a large specimen, in which no plications are developed. The 

 surface presents well-marked concentric striee, and obscure longitudinal striae on the 

 ventral valve. 



1 m. A dorsal valve which is strongly plicate, but shows no mesial sinus. 



1 n, 0. Specimens showing the plications developed upon the mesial portion of the shell in 

 very different degrees of strength. 



1 p. Profile of the specimen 1 o. 



1 q, r, t. Dorsal, profile and front views of a specimen having plications only on the mesial 

 fold and sinus. 



1 t, u. Dorsal views of specimens with plications developed over the entire surface of the 

 valves; the one with, and the other without a mesial sinus. 



1 w. An individual showing bifurcating and coalescing strise. 



1 X. Profile of the specimen 1 w. 



1 y, z. Front views of specimens, the one with and the other without a mesial sinus. 



