226 



Meristella barrisi. Hall. (Fig. 1 *I~> A. ) (Pal. N. V.. 

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



Distinguishing Characters. — Gibbous form; rather closely 

 incurved beak of pedicle valve, which overarches that of 

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

 shells produced into a short, linguiform extension: abrupt 

 elevation near anterior margin of brachial valve: smooth or 

 concentrically striate surface. 



Found in the Hamilton group of Erie County. (Coll. Am. 

 Mus. Nat. Hist. New York. ) 



Genus ATRYPA. Dalman. 



[Ety. : A, without ; trypa, foramen ; erroneously applied.] 



(1828: Kongl. Veteuskaps. Akad. Haudlingar., 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 or sometimes slightly concave, from 

 the strongly-marked sinus. Beak of the pedicle valve small 

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

 rated and doubly -grooved teeth are present, unsupported 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. (Linnaeus.) (Fig. 136.) (Pal. 

 X. 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, ;it Sections 4 and 5 (common): Stictopora and 

 Demiss.-i beds, at Section 5 (abundant); shale down to nine 

 feet below the Encrinal limestone (rare). 



