226 



Meristella bakkisi. Hall. (Fig. 13oA.) (Pal. N. Y.. 

 Vol. IV., p. 304, PI. LXIX. ) 



Distinguishing diameters. — Gibbous form; rather closely 

 incurved V)eak of jjedicle valve, which overai-ches that of 

 brachial valves; pedicle valve depressed in front, and in old 

 shells produced into a short, linguiform extension : abru})t 

 elevation near anterior margin of brachial valve; smooth or 

 concentrically striate surface. 



Found in the Hamilton grou]) of Erie County. (Coll. Am. 

 Mus. Nat. Hist. New York. ) 



Genus ATRYPA. Dalmax. 



[Ety. : ^1, without ; trypu, foramen; erroueously applied.] 



(1828: Kongl. Veteuskaps. Akad. Haudliugar., p. 127. 1893: Pal. N. Y.. 

 Vol. VIII., Pt. II., p. 163.) 



Shell varying in outline from nearly circular to longitudi- 

 nally sub-oval. Valves very unequal, brachial valve being 

 strongly convex or gibbous, while the pedicle valve is gently 

 convex or almost flat c^r sometimes slightly concave, from 

 the strongh^-mai-ked sinus. P)eak of the pedicle valve small 

 and incurved over that of the brachial. Large widely-sepa- 

 rated and doubly -grooved teeth are present, unsup]jorted by 

 lamellae. Strong muscular impressions. Spirals of the 

 brachidium, with their bases parallel to the inner surface of 

 the pedicle valve, and the apices directed towards the deepest 

 point of the opposite valve. Surface radially plicate. 



Atrypa reticularis. (Linna3us.) ( Fig. 136. ) ( Pal. 

 N. Y., Vol. IV., p. 316, Pis. LI.-LIII.A.) 



Distinguishing Characters. — Great convexity of brachial 

 and slight convexity of pedicle valve ; rounded bifurcating 

 surface plications, reticulated by concentric striations. 



Found in the lower Moscow shale, especially in the coral 

 layer, at Sections 4 and 5 (common): Stictopora and 

 Demissa beds, at Section 5 (abundant) ; shale down to nine 

 feet below the Encrinal limestone (rare). 



