CAMAROTCECHIA 175 



The surface is marked only by concentric lines of growth which are 

 irregularly developed, frequently being obscure or wholly obsolete. 



Remarks. In its general form this species resembles members of the 

 rhynchonelloid genus Pugnax, but it differs fundamentally from members 

 of that genus in having a distinct spondylium in the pedicle valve sup- 

 ported by a median septum. This septum, and also that of the opposite 

 valve, is almost always clearly recognizable, except in silicified specimens, 

 as a dark line extending anteriorly from the beak. Hall and Clarke re- 

 ferred the species to Pugnax doubtless because the specimen which they 

 studied and illustrated was a very perfect sulphur cast of McChesney's 

 type specimen, but upon which there was, of course, no color differentia- 

 tion which would lead to the recognition of a septum. 



The species is very distinct from all other members of the genus in om' 

 American Mississippian faunas, and can be confused with none of them. 

 It occurs abundantly in some of the Chester faunas where it is a highly 

 characteristic species. 



Horizon. Chester group. 



Order TELOTREMATA 



Family RHYNCHONELLID^E 



Genus CAMAROTCECHIA Hall and Clarke 



Description. Shell rhynchonelliform, small or below medium size, 

 subovate, subpentangular or subtriangular in outline. The mesial fold 

 and sinus well developed, the surface of both valves marked by angular 

 or subangular plications which extend to the beak, the plications not 

 medially grooved in front. In the pedicle valve the hinge-teeth are 

 rather small and are supported by slender, vertical, dental lamellae. In 

 the brachial valve a well-defined median septum is present in the rostral 

 portion of the valve which is divided internally to form a V-shaped crural 

 cavity, the hinge-plate is divided, the inner margin of each lateral portion 

 being supported by one of the lateral walls of the crural cavity; no car- 

 dinal process is present and the crura are formed by the anterior extension 

 of the inner margins of the two divisions of the hinge-plate. 



Remarks. The essential generic characters of Camarotoechia are found 

 in a combination of the internal and external features of the shell. The 

 median septum of the brachial valve supporting the V-shaped crural 

 cavity and the divided hinge-plate are identical in all essential respects 

 with the rostral characters of Wilsonia, Liorhynchus, Paryphorhynchus 

 and Pugnoides, the five genera being differentiated one from another 

 by constant external characters. In Wilsonia the shell is subcubical in 

 form with the plications flattened anteriorly and longitudinally grooved, 

 especially in the fold and sinus. Liorhynchus is a larger shell with the 



