224 



Distinguishing Characters. — Robust character ; size ; 

 "shouldered" expression; greater convexity of brachial 

 valve; "nasiite" front, caused by deep sinus; coarse surface 

 lamellae; outline of muscular impressions. 



Found in the upper Moscow shale, two feet below the 

 Styliolina band, at Section 3 (very rare); lower Moscow 

 shale, at Sections 4 and 5 (common); Encrinal limestone, 

 at Section 5 (common); Lower shales (fairly common below 

 the Demissa bed, abundant nine feet below the Encrinal lime- 

 stone — A. spiriferoides bed); also twenty feet below the 

 Encrinal; also in the Modiomorpha suhalata bed; it is again 

 abundant in the shale between the lower and middle Trilobite 

 layers; and occurs as low as the Nautilus bed, and the 

 sliales below it. 



Gent s MERISTELLA. Hall. 



[Ety. : Diiniiiutive of Merista ; mews, apartment (chamber).] 



(1860 : 13th Rcp't X. Y. State Cab. Nat. Hist., p. 74. 1893: Pal. N. Y., 

 Vol. VIII., Pt. II., p. 73.) 



Shell unequally biconvex, often inflated, varying from 

 transverse to elongate in outline; cardinal areas obscure. 

 Anterior margin sinuate, caused by sinus and fold, which 

 appear only near the front of the shell. Umbo of the pedicle 

 valve incurved at maturity, concealing most, if not all, of 

 the foramen. Teeth strong, supported by lamellge; deep, 

 sub-triangular muscular impression in pedicle cavity. In 

 the brachial valve a median septum supports the hinge 

 plate, and extends foi' somewhat more than one-third the 

 length of the shell. Brachidium a spire. 



■^^^^^ ^ ?V 



Fig. 134. MeristeUa hMskinsi. Dorsal, profile, and ventral views of a specimen (from 

 Hall;. 



