BRA CHIOPODA—PROTREMA TA. 271 



217. S. calcifera (Billings). (Fig. 325.) Upper Cambric. 

 Brachial valve triangular posteriorly. Moderate sinus in pedicle 



valve and fold on brachial. Surface marked by concentric growth 

 lines only. Average length about ^ inch. 



Saratogan, etc., of Mis- 

 souri, Utah, Nevada, Quebec, 

 Newfoundland. 



LXII. Camarella Billings. 



Small, smooth in the um- ,*__ „„^ c , ^- t v a- i a 



' PlG. 325. Syntrophia calcifera, pedicle and 



bonal region with a few low brachial valves. (After Walcott.) 



plications anteriorly ; no car- 

 dinal areas. Pedicle valve with erect beak and an open delthy- 

 rium. Well-defined spondylium present. Brachial valve at ma- 

 turity the more convex. Median sinus on pedicle valve and fold 

 on brachial. Ordovicic-Siluric. 



218. C. varians Billings. (Fig. 326.) Ordovicic. 



Subtriangular. Valves mod- 

 erately and equally convex. 

 Anterior angles rounded. Pli- 

 cations rounded, 6-8, of which 

 -c r r n tr a- 2-4 occupy the mesial sinus and 



FlG. 326. Camarella varians (Canadian ^ rJ 



Surv.). 3-5 the fold. Length about y^ 



inch, width about the same. 

 Beekmantown-Chazy of New York, Newfoundland, Mingan 

 Islands. 



LXIII. Parastrophia Hall and Clarke. 

 Subcircular. Hinge line moderately long and straight. No 

 cardinal areas. Brachial valve the larger and more convex, its 

 beak projecting conspicuously beyond that of the pedicle valve. 

 Otherwise much like Camarella. Ordovicic-Siluric. 



219. P. hemiplicata Hall. (Fig. 327.) Ordovicic. 

 Subglobose, wider than long, with thickness often equal to length. 



Hinge line short. Pedicle valve depressed convex with an abrupt 

 broad sinus. Brachial valve very convex with a broad median 

 fold. Surface marked by about 6-8 plications, strong toward the 

 front but fading away entirely toward the umbo. 2-3 plications 

 occupy the sinus and 3-4 the fold ; all are crossed by concentric 

 lines. 



