220 



Foinid in the lower Moscow shale (?); Stictopora and 

 Demissa beds, at Section 5 (common) ; four to five feet below 

 the Encrinal limestone, at Section 6 (very rare); nine to 

 twelve feet below the Encrinal limestone, at Section 7 (very 

 rare); shale below the Trilobite beds, in Avery's Creek 

 (rare) ; Plenrodictyum beds and Calcareous bed above them, 

 in Avery's Creek (rare). 



Cyrtina hamiltonensis, var. recta. Hall. (Fig. 130.) 

 (Pal. X. Y., Vol. IV.. ].. 270, PI. XLIX.) 



Distinguishing Char- 

 W-'^M t^, arte vs. — Plane flat 



^{Mt j:.=^A;.:A area; angular plica- 



FiG. 130. Cyrtina hamiltonensis, var. recta. Dorsal, tlOUS ; beak UOt lU- 

 ventral, and cardinal views (from Hall). , 



curved. 

 Found in the upper Plenrodictyum bed (rare). 



Genus PARAZYGA. Hall and Clarke. 



[Ety. : Para, beside; ^ygos, yoke.] 

 (1893: Pal. K Y., Vol. VIII., Pt. II., p. 127.) 



Shells transverse, biconvex; valves nearly equal, with 

 median fold and sinus. Umbo of pedicle valve closely in- 

 curved. No hinge area. Surface covered with numerous 

 fine, rounded, simple ribs, extending alike over median fold 

 and sinus, and bearing short hair-like spines, which are 

 commonly broken off, leaving only their bases. Brachidium 

 a spire. 



tew 



Fig. 131. Parazyga hirsutn. Dorsal, ventral, profile, cardinal, and front views (from 

 Hall). 



