PLATE 97. 



Pag. 



Fig. la-k, &2a-i. Spirifer arrectus. 422 



1 a, b. Dorsal and front views of a specimen in which tlie sliell is partially exfoliated. ( The 

 mesial fold is more angular in the specimen tlian is represented in the figure.) 



1 c. The ventral valve of another specimen, in which the plications are rounded. 



1 e. A ventral valve which is more extended on the hinge-line, and preserves to a considerable 

 degree the surface markings, and has about eight plications on each side. 



If. A dorsal valve of proportionally greater length : the plications are broad and rounded, 

 and seven are visible on each side. 



1 g. Profile view of a gibbous specimen. 



1 h. An enlargement of the surface, showing the fine concentric and radiating stri» as they 



appear on a worn surface. 



2 a. The dorsal side of a cast, in which the plications are sharply angular. 



2 b, c, d, e. Casts of the ventral valve, showing a variety of form and markings in the cast of 

 the muscular impression, and in the number and development of the plications. 



2/. Cardinal view of a cast whicli is somewhat distorted, and shows a part of the ventral 

 valve ; the beak is broken ott". 



2 g. A cardinal view of the cast of a ventral valve, showing the elevation of the process filling 

 the beak. 



2 A. A similar view, showing also the ventral side and the median line. 



2 t. The cast of a distorted specimen. 



