BRACHIOPODA — TELOTREMATA. 



3C9 



XCVIII. Cyclospira Hall and Clarke. 

 Subquadrate. Pedicle valve very convex with a prominent, in- 

 curved umbo and keeled posteriorly with a median sinus anteriorly. 

 Brachial valve depressed, bearing a low median fold anteriorly; 

 cardinal process small, supported by a low median septum. 

 Brachidium very simple (Fig. 386, h). Surface smooth. Ordovicic- 

 Siluric. 



310. C. bisulcata (Emmons). (Fig. 386, d-h.) Ordovicic. 



Small. Beak of pedicle valve defined on each side by two ele- 

 vated ridges curving to the lateral margins of the valves. 



Trenton of New York, Minnesota, Ontario, Manitoba. 



I 



XCIX. Atrypa Dalman. 

 Subcircular, strongly inequivalved. Hinge line short. Brachial 

 valve very gibbous. Pedicle valve much less convex or nearly flat 

 with a small, incurved beak and bearing a median sinus. Teeth 

 large and widely separate. Muscu- 

 lar impressions strong. Spirals di- 

 rected dorso-medially ; jugum in 

 extreme posterior portion. Surface 

 radially plicate. Siluric - Missis- 

 sippi. 



311. A. nodostriata Hall. (Fig. 

 387.) Siluric. 



Valves subequal. Surface nod- 

 ulose because of the lamellose growth 

 lines. 



Clinton and Niagaran of New 

 York, Ohio, Kentucky, Wisconsin. 



312. A. marginalis (Dalman). 



Siluric. 



Length and breadth subequal. Beak of pedicle valve incurving 

 over, but not covering that of the brachial valve. Both valves 

 convex, the pedicle with a well-marked median sinus, bounded on 

 each side by one or two stronger plications, and the brachial with 

 a correspondingly well developed fold. Entire surface marked by 

 radiating plications, which are crossed by concentric striae; these 

 latter are often obsolete. 



Niagaran of Kentucky, Tennessee, Ohio, Indiana, Illinois. 



f 



Fig. 387. Atrypa nodostriata, 

 with stride enlarged (Pal. N. Y. 

 II.). 



