BRACHIOPODA — TELOTREMATA. 283 



valve. Pedicle valve at first with a median fold which later be- 

 comes a sinus ; the brachial valve likewise reverses its early me- 

 dian sinus into a fold. Two elevated and longitudinally striated 

 deltidial plates fill the delthyrium. Siluric. 



244. R. cuneata americana Hall. (Fig. 344.) Siluric. 



Wedge-shaped. Beak of pedicle valve angular with compressed 

 sides. Deep frontal emargination extends as a broad sinus two 

 thirds of the distance to the beak. 

 Plications crossed by threadlike concen- 

 tric striae. 



Niagaran of New York, Kentucky, 

 Indiana, Wisconsin, Ontario. 



Fig. 344. Rhynchotreta 



cu- 



neata var. americana (Pal. 



lt. 



Y., II.). 





LXXVI. Camarotgechia Hall and 

 Clarke. 



Rhynchonelloid, rostrate. Brachial 

 valve the deeper. Pedicle valve shal- 

 low with beak projecting over that of the 

 brachial. Surface radially plicate. Dis- 

 tinctive internal characters are : a median septum in the brachial 

 valve, dividing posteriorly to form an elongate spondylium, no car- 

 dinal process. In the pedicle valve slender vertical lamellae sup- 

 port the teeth. Ordovicic-Mississippic. 



A. Small — less than y z inch wide *. 



* Length and width nearly equal i. 



1. Round posteriorly 254. C. dotis. 



1. Acute posteriorly a. 



a. Fold and sinus very conspicuous 246. C. neglecta. 



a. Fold and sinus inconspicuous 252. C. semiplicata. 



* Length exceeding width 247. C. acinus. 



* Width exceeding length. Surface rugose 250. C. lamellata. 



B. Of medium size — ]/ z inch or more wide **. 



** Transversely oval, i. e., width exceeding length 2. 



2. Plications angular, numerous (20-24), of which 4-7 mark the mesial sinus 



and fold b. 



b. Plications coarse and prominent 256. C. sappJw. 



b. Plications fine 255. C. Jiorsfordi. 



2. Plications obtuse, few (about 16), of which 2 or 3 mark the sinus and 

 fold 258. C. sageriana. 



** Somewhat quadrangular, i. <?., with length and breadth nearly equal 3. 



3. Both valves noticeably convex c. 



c. Plications numerous (14-20) 1/. 



I 7 . Shell ventricose, thickness equal to or greater than length. 



272. C. ( Wilson ia) ventricosa. 



