310 PALEONTOLOGY OF NEW YORK. 



Gends CHONETINA, Krotow. 1888. 



1884. Chonetella, Krotow (not Waagen). Artinskische Etage, p. 274. 

 1888. Chonetina, Kkotow. M6m. du Comite G6ologiqne, vol. vi, p. 500. 



A brief description of the characters of this genus* has been given by 

 (EHLERT,t from which it appears that " Chonetina differs from Chonetes by its 

 very convex ventral valve, having a profound sinus ; the small valve, very 

 concave, follows the curvature of the larger ; in the interior of the dorsal valve 

 are tubercles arranged in radiating series which unite to form high, compact 

 lamellae, extending from the beak to the anterior margin ; two of these, more 

 prominent than the rest, limit the surface occupied by the sinus of the larger 

 valve. The type, C. artiensis, Krotow, belongs to the horizon of the Artinskian 

 grit (Permian)." 



Without actual knowledge of the specimens upon which this separation from 

 Chonetes has been based, it may be imprudent to express an opinion as to the 

 value of the proposed genus. The American species which are deeply sinused 

 on the pedicle-valve, e.g., Chonetes Verneuiliana and Ch. mesoloba, Norwood and 

 Pratten, show no valid grounds for separation from Chonetes. 



Genus CHONOSTROPHIA, gen. nov. 



PLATE XV B, FIGS. l-HD ; AND PLATE XVI, FIGS. 13,29. 



1857. Chonetes, Hall. Tenth Rept. N. Y. State Cab. Nat. Hist., p. 56. 



IS.'JG. Chonetes, Hall. Palaeontologpy of N. Y., vol. iii, p. 418, pi. xciii, figs, la-d, 2c. 



1882. Chonetes, Whitfield. Annals N. Y. Academy of Science, vol. ii, p. 213. 



1S83. Choyietes, Hall. Rept. N. Y. State Geologist for 1882, pi. xvi, figs. 13, 29. 



Diagnosis. Shell reversed, concavo-convex, the pedicle-valve being slightly 

 convex about the umbo, but becoming broadly concave over the pallial region. 

 Outline and contour strophoraenoid ; valves extremely tenuous and compressed ; 

 surface covered with fine, alternating or fasciculate striae. In the pedicle-valve 

 the upper margin of the cardinal area bears a row of hollow spines of the same 

 structure and arrangement as in Chonetes. The delthyrium is narrow and 

 appears to be more or less completely closed. The teeth are quite strong and 



* The original descriptions of both genus and species are in the Russian language. 

 t L'Annuaire g^ologique universe!, vol. v, p. 1152. 1889. 



