PLATE 97. 
Page 
Fig. 1 a - A, & 2 a - i . Spirifer arrectus. 422 
1 a. b. Dorsal and front views of a specimen in which the shell is partially exfoliated. (The 
mesial fold is more angular in the specimen than is represented in the figure.) 
1 c. The ventral valve of another specimen, in which the plications are rounded. 
1 c. 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. 
1 f. 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 stria; 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. 
2f. Cardinal view of a cast which is somewhat distorted, and shows a part of the ventral 
valve ; the beak is broken off. 
2 g. A cardinal view of the cast of a ventral valve, showing the elevation of the process filling 
the beak. 
2 h. A similar view, showing also the ventral side and the median line. 
2 i. The cast of a distorted specimen. 
