200 



I>isTinguishin<j; Characters. — Medinni to laj-ge size: slight 

 convexity; surface strifie distant, increased by intercalation, 

 and between these are very fine striiP, crossed by fine con- 

 centric strict; muscular area in brachial valve defined bv 

 thickened rounded ridges, divided by central rounded ridge 

 extending from the bifid cardinal ])rocess. and dividing ante- 

 riorly. 



Found in the Demissa bed, at Section 5 (a few specimens 

 only ). 



Stkopheodoxta I'LK ATA. Hall. (Fig. 104. ) (13th Ann. 

 Kep't N. Y. State Cab. Nat. Hist., p. 90. Pal. 

 X. Y., Vol. IV.,P1.LXHI.) 



Distinguishing Chanicters. — Small size ; 

 strong rounded or sub-angular plications, 

 ^ ,^, „ ^ which increase in number towards the front 



Fig. 104. Strophe- 



?erior" of """bracWai ^7 implantation. These readily distinguish 

 nai^rowss^'broken "this specics froui S. dewissa, its nearest ally. 

 fa'l-gea, fromlguua- Fouud ouly iu the Demissa bed, at Section 



l>efcha east. COrigi- _ / , -, 



iiai.) .) (not common). 



Gexus CHONETFS. Fis( hi:i; ni: ^VALIJHEIM. 



[Ety. : CJione, ;i funuel.] 



(1837: Oryctographie du Gouv. de Moscow, Pt. II., p. 134. 1892: Pal. 

 N. Y., Vol. VIII., Pt. I., p. 303.) 



Shells concavo-convex (in our species), with the pedicle 

 valve convex. Outline varying from semi-circular to semi- 

 oval; liinge line straight, making the greatest diameter of 

 the shell. Areas narrow; the triangular opening (delthy- 

 rium) in the area of the pedicle valve covered by a convex 

 pedicle plate (deltidium). The upper margin of the are;i 

 bears a single row of hollo^y spines. Area of brachial vahe 

 without spines. Cardinal process appearing quadrilobate. 

 Interior of shell strongly papillose in the pallial region. A 

 low median ridge divides the muscular area of the })edicle 

 valve. A similar ridge occurs in the brachial valve. Exter- 

 nal surface usually covered bv radiatint!' st]-i;e. 



