PLATE XXXV. 



(Figures 1-29 by R. P. Whitfield.) 



Legend ; D. Deltidial plates. j. Cardinal process. 



/I. Delthyriuin. b. Dental sockets. 



F. Foramen. c. Crura, 



t. Teeth. a. Anterior adductors, 



d. Dental lamellae. a'. Posterioi- adductors. 



X. Pedicle-cavity. r. Diductors. 



s. Median septum. 



Grnus SPIRIFER, SowEKiiY. 



Page 1. 



Spirifer sulcatus, HLsinger. 



Fig-. 1. An inilividual of normal proportions ; showing- the lamellose exterior. 



Figs. 2, 3. Enlargements of the central portion of the cai-dinal area of two examples. The deltidial plates 



have not united in either sjiecimeu, but have attained a more adv.anced development in fig. 2 



than in fig. 3. 

 Fig. 4. Enlargement of the external laraellose suvfai:e ; showing the minute pustules on the radial stria- 



tions. 



Niagara group. Lockport, N. Y. 



Spirifer karicostus, Coiirad. 



Fig. 5. A brachial view of a specimen of ordinary size. 



Fig. 6. An enlai'geiuent of the surface of the same specimen ; .showing the inequidistant lamellae. 

 Corniferous limestone. Central Kew Ym-k. 



Spirifer perlamellosus, Hall. 



Fig. 7. A normal adult shell, retaining the deltidial covering and foramen. 



Fig. 8. A median longitudinal section of conjoined valves ; showing the dental plates and median septum 



of the pedicle-valve and the crura of the brachial valve. 

 Fig. 9. -An enlargement of the external surface ; showing the crowded and radially striated lamellae. 

 Fig. 10. An enlargement of the central portion of the cardinal area, bearing a perforated deltidial covering 



in which the plates .are completely coalesced and extend to the beak of the brachial valve. 

 Fig. 11. A similar enlargement from another specimen, having a shorter deltidial covering. 

 Fig. 12. The interior of a pedicle-valve ; showing the imperforate deltidial covering and the median 



septum. 

 Fig. 13. An enlargement of the central jiortion of a brachial valve ; showing the crura and the peculiar 



bilobed form of the cardinal process lying at the base of the socket-walls. 

 Lower Helderberg group. The Helderhergs, N. Y. 



Spirifer raricostus, Conrad. 



Fig. 14. An enlargement of the central portion of the cardinal area ; showing its transverse striation and 

 the incipient deltidial plates. 



Corniferous limestone. Albany county, N. Y. 

 Fig. 15. An oblique view of the pedicle-valve ; showing the median septum. 



Corniferous limestone. Western New York. 

 Fi". 16. The interior of a pedicle-valve of a small individual ; showing the teeth and low septum. 

 Fi". 17. An internal cast of a pedicle-valve ; showing the filling of the rostral cavity, the position of the 

 median septum and the impression of the muscular scars. 

 Schoharie grit. Albany county, N. Y. 



