PLATE 46. 
1 a - z. Pentamertjs galeatus. 
1 a, b, c. Young shells which are free from plications. 
1 d, e, f. Views of a young specimen which has become very gibbous, and with plications 
strongly developed upon the mesial fold. 
1 g, li, i. Three figures of half-grown individuals, showing the different degrees of develop¬ 
ment in the plications. 
1 k, l. Dorsal and front views of a large specimen, in which no plications are developed. The 
surface presents well-marked concentric striae, and obscure longitudinal stria: on the 
ventral valve. 
1 m. A dorsal valve which is strongly plicate, but shows no mesial sinus. 
1 ii, o. 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, s. 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 striae. 
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. 
