228 



Found in the lower Moscow slialew, at Sections 4 and 5 

 (rare); Encrinal limestone (?), at Section 5; Stictopora and 

 Deinissa beds, at Section 5, etc. (abundant); Lower shales, 

 occasionally down to the Nautilus bed, at Sections 5 to 8 ; 

 and on the Lake Shore. 



Genus ATHYRIS. McCoy. 



[Ety. : .1, without; thyris, small door, i. e., absence of deltidial plates; 

 erroneously applied.] 



(1844 : Synopsis Carbon. Foss. Ireland, p. 128. 1893: Pal. X. Y., 

 Vol. VIII., Pt. II., p. 83.) 



Shell biconvex, with the valves nearly equal : outline vary- 

 ing from sub-circular to transversely elliptical. Pedicle valve 

 with the beak incurved, the pedicle opening and deltidial 

 plates usually concealed. Teeth prominent, recurved at 

 the tips, and supported by stout dental lamelkie. Strongly- 

 marked muscular impressions. Brachial valve with the 

 beak small, the dental sockets broad and deep, and the hinge 

 plate strong, and perforated by a "visceral foramen." 

 Brachidiiim consisting of spiral cones placed base to base. 

 Surface lamellose. the pedicle valve marked by a shallow 

 sinus, and the bi*achial l)y a corresponding gentle elevation. 



Athyris spirifekoides. (Eaton.) (Fig. 133.) (Pal. 

 X.Y., Vol. IV.. p. 285. PI. XLVL) 



-%~.. 



Fig. 1.33. Athyris spiriferoides. Dorsal, ventral, cardinal, and front views of a charac- 

 teristic specimen (from Hall). 



