610 Forty-fifth Report on the State Museum. 



(?) Subgenus Chonetina, Krotow. 1888. 



These shells differ from Chonetes in their very convex pedicle- 

 valve having a profound sinus ; the brachial valve, very concave, 

 follows the curvature of the larger ; in the interior of the brachial 

 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, 

 imit the surface occupied by the sinus of the larger valve. 



(Type, C. Artiensis, Krotow. Permian.) 



Subgenus Chonostrophia, Hall. 1892. 

 (Plate 20, Figs. 20-24.) 



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

 convex about the umbo, but becoming broadly concave over the 

 pallial region. Outline and contour strophomenoid ; valves 

 extremely tenuous and compressed ; surface covered with fine 

 alternating or fasciculate strise. 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 rest upon the bottom of 

 the valve ; between them arises a low median septum which may 

 be traced from one-third to one-half the length of the valve, 

 dividing a subcordate muscular area, the outer margins of which 

 are distinctly elevated. 



In the brachial valve the crural plates are united to form a 

 bilobed cardinal process. The outer face of this process has not 

 been observed ; on the inner surface it is not continued into a 

 median septum but ends abruptly. Muscular area very faintly 

 defined in the type-species. Internal surface over the pallial 

 region finely papillose. Shell-substance fibrous, punctate. 



(Type, G. reversa, Whitfield (sp.). Lower Devonian.) 



Subgenus Chonetella, Waagen. 1884. 



Shell small, normally concavo-convex. Surface rounded, with 

 radial strise; cardinal area narrow ; deltidium, cardinal spines and 

 teeth as in Chonetes, hi the pedicle-valve the adductor impres- 



162 



