472 MISSISSIPPIAN BRACHIOPODA 



beak small, moderately incurved. Internally the cardinal process is very 

 broad and thick, and is coalesced with the socket plates, the hinge 

 sockets being excavated from its sides, its main surface lies nearly 

 parallel to the plane of the valve, is subcrescentic in outline, with a 

 raised margin posteriorly and laterally, anteriorly the surface drops 

 abruptly to the floor of the valve, the lateral margins are extended 

 farther anteriorly than the median part and doubtless bear the crura; 

 the muscular scars smaller and a little more deeply excavated and 

 more sharply defined than those of the opposite valve, divided longitud- 

 inally by a faint median septum. 



Surface of both valves smooth, or nearly smooth, marked only by 

 more or less indistinct, concentric lines of growth. 



Remarks. The generic relations of this shell are uncertain. It is 

 not a true member of the genus Atkyris, neither can it be placed in another 

 genus with any more certainty. It is not unlikely a representative of an 

 undescribed genus, but the character of its brachidium should be known 

 before defining it as new. For the present, therefore, it may be allowed 

 to remain in Athyris, where it was originally placed by the author of the 

 species. 



Horizon. Upper Kinderhook. 



Genus CLIOTHYRIDINA Buckman 



Description. Shells small, of medium size or large, from subcircular 

 to transversely subelliptical in outline, mesial sinus of the pedicle valve 

 and fold of the brachial valve well developed or obsolete, the surface 

 of the valves marked by broad, thin, lamellar extensions, which are divided 

 nearly or quite to their bases into long, flat spines. The beak of the pedicle 

 valve usually incurved so as to conceal the foramen and delthyrium in the 

 mature shells, the dental lamellae and muscular scars as in Athyris. 

 In the brachial valve the hinge-plate and brachidium are similar to the 

 same structures in AtJtyris. 



Remarks. This generic group has been called Cliothyris by Hall and 

 Clarke, 1 on King 's authority, and authors have commonly used that name 

 since the publication of their work. It has been shown by Buckman,: 

 however, that the name Cliothyris must be accredited to Phillips and if 

 used at all must be considered as a synonym of Athyris, over which it has 

 priority, and he has proposed the new generic name CUothyricKna to 

 designate this group of shells. The genus differs from Atliyris, as used in 

 this work, in the form of its surface markings, the concentric lamellae 

 developed from the lines of growth being divided into flat spines by 

 deep incisions. These fringe-like lamellae are commonly more or less 



1 Pal. N. Y., vol. 8, pt. 2, p. 90. (1894.) 



2 Ann. and Mag. Nat. Hist, ser. 7, vol. 18, p. 321 (1906). 



