PLATE XXXIV. 



(Figures 1-33 by R. P. WHITFIELD.) 



Legend : A. Cardinal area (outer division). j. Cardinal process. 



A'. Cardinal area (inner division). b. Dental sockets. 



A. Delthyrium. c. Socket-walls, 



s'. Delthyrial callosity. s. Median septum. 



t. Teeth a. Adductor scars. 



d. Dental lamellse. r. Diductor scars. 



Genus SPIRIFER, Sowekby. 



Pajfe 1. 



Spiuifer macrus, Hall. 



Fig. 1. The exterior of a pedicle-valve ; showing the lamellose character of the surface. 



Corniferous limestone. Western New York. 

 Fig. 2. A cardinal view of an interaal cast of the pedicle-valve. 

 Fig. 3. An internal cast of the pedicle-valve ; showing the size of the muscular impression. 



Schoharie grit. Schoharie, N. Y. 



Spirifer varicosus, Hall. 



Fig. 4. A brachial valve ; showing the character of the external surface. 



Fig. 5. A cardinal view ; showing the height of the cardinal area and the width of the delthyrium. 



Fig. 6. The interior of a brachial valve ; showing the articulating apparatus. X 2. 



Fig. 7. The interior of a portion of the pedicle-valve with a highly developed delthyrial callosity. 



Fig. 8. An enlarged view of another specimen showing the same structure. 



Upper Helderberg group. Williamsville and western New York. 



Spirifer consobrinus, d'Orbigny ( = Spirifer zic-zac, Hall). 



See Plate 35. 

 Fig. 9. A normal adult ; showing the lamellose exterior, and the sulcus on the median fold. 

 Hamilton group. Western New York. 



Spirifer arctisegmentus, Hall. 



Fig. 10. A pedicle-valve, viewed from the apex. 



Fig. II. A cardinal view of the same specimen; showing the height of the area, its outer and inner divi- 

 sions, and the form of the delthyrium. 

 Fig. 12. An enlargement of the lamellose external surface. 



Hamilton group. Clarke county, Indiana. 



Spirifer mucronatus, Conrad. 



A specimen of the usual form and proportions in the soft shales ; showing the lamellose exterior. 

 A shorter and more rotund specimen. 



Hamilton group. Canandaigua Lake, N. Y. 

 A small pedicle-valve with highly extended cai'dinal extremities. 



Marcellus shales. Near Alden, N. Y. 

 A specimen with long, narrow, acuminate cardinal extremities. This is a somewhat unusual form. 



Hamilton gi'oup. Darien Center, N. Y. 

 The interior of a brachial valve ; showing the articulating apparatus and muscular area. 

 The interior of a pedicle-valve ; showing the teeth and muscular area. 



An enlargement of a portion of the brachial valve ; showing the detailed structure of the dental 

 sockets, cardinal process and adductor musculai- scars. 

 Fig. 20. A similar enlargement of the corresponding parts of the pedicle-valve, the muscular impressions 

 being much broader than in the preceding specimen. 



