BRACHIOPODA. 213 



short, while the supporting septum is carried beyond it, sometimes to nearly 

 one-half the length of the shell. Near the teeth, which are small, there are 

 two accessory supporting lamellae abutting on one side against the outer surface 

 of the converging dental plates, and on the other against the interior cardinal 

 surface of the valve ; thus enclosing small lateral umbonal cavities. Muscular 

 scars of this valve always obscure. 



In the brachial valve the cardinal plate is narrow, subtriangular, in the 

 typical species bearing a very small cardinal process, which in other species is 

 rarely present. The hinge-plate is traversed by two tine, divergent ridges 

 running outward from the beak and continuous beyond the anterior edge of 

 the plate into long, slender and upwardly curving crura. Beneath the crura 

 arises a broad, shallow, trough-shaped plate, which, near the apex, is supported 

 by a short median septum resting on the valve. This process is strongly curved 

 toward the opposite valve and is continued for most of its length beyond 

 the termination of the median septum. Usually it widens outwardly, and then 

 narrows rather abruptly, or even acutely, to its extremity. The adductor 

 muscular scars are well developed in this valve, forming a broadly oval or sub- 

 circular impression. 



Vascular sinuses are sometimes retained on both valves. 



Type, TerebratuHtes Schlotheimi, von Buch.* Permian. 



Observations. According to our present knowledge, this genus represents the 

 latest appearance of the camarellid interior. Its relations to the various groups 

 of the rhynchonellids is largely, and we may say with a single reservation, 

 wholly external. Species of Camarotcechia do develop, in the brachial valve, 

 an elongate cavity on the summit of the median septum ; this is always in an in- 

 cipient condition and is attained quite independently of any association with, or 

 derivation from Conchidium and its allies. From this source may have come the 

 brachial spondylium of Camarophoria, though the mode of attachment beneath, 

 instead of in continuity with the hinge-plate, may perhaps render such assump- 



* Davidson, at various times, expressed the opinion that this specific tei'm should be regarded as a syn- 

 onym foi- Martin "s CtmchylioVithus anmnltes crumena, fi-om the Cavljoniferons limestone. Thei-e are some 

 differences in the two shells as described and illustrated by Mr. Davidson, and as the typical forms of each 

 are from distinct faunas it is wiser to keep them apart. ^The Permian shell is the type of Camaropjiobia. 



