220 



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

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

 the Encrinal limestone, at Section (> (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); Pleurodictyum beds and Calcareous bed above them, 

 in Avery's Creek (rare). 



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

 (Pal.N. V.. Vol. IV.. p. 270, PI. XLIX.) 



Distinguishing Char- 

 acters. — Plane flat 

 ^ area; angular plica- 



Fio. 130. Cyrtina hamiltonensis, var. recta. Dorsal, tioilS ; beak IlOt ill- 

 ventral, and cardinal views (from Hall). 



curved. 

 Found in the upper Pleurodictyum bed (rare). 



Genus PARAZYGA. Hall and Clarke. 



[Ety. : Para, beside; zygos, yoke.] 

 (1893: Pal. N. 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 s | lire. 



Hill' ' ''' / '"'" '""" / '"' s "'" '»orsal, ventral, profile, cardinal, and front views (from 



