PLATE 22. 



Fig. 1 a- t. Strophodonta beckii. 



1 o. A young individual in which no corrugations are developed. 



1 b, c. Two specimens exhibiting the extremes of form in the extension of the hinge-line, and 

 showing the beginning of the development of the corrugations. 



1 d. A specimen showing the corrugations more strongly. 



1 e. An individual of full size, in which the corrugations are well developed. 



1/, g. Dorsal and ventral sides of an entire individual. 



1 h. Profile view of the preceding specimen. 



1 t. An old specimen where the corrugations are much stronger and closer than usual. 



1 k, I, m. The interiors of several ventral valves, showing the area, crenulated hinge-line, 

 muscular and vascular impressions, etc. 



1 n. Area of the ventral valve. 



1 0, p. Enlargement and profile of the strise. 



1 r. A portion of the area enlarged, showing the striated surface and crenulated margin. 



1 s, t. Portions of the casts of the ventral valves of two different individuals, showing some 

 slight difference in the character and strength of the impressions. 



Pa^e 



191 



