200 



Distinguishing Characters. — Medium to large size: slight 

 convex it v : surface striae distant, increased by intercalation, 

 and between these are very fine stria?, crossed by fine con- 

 centric stria?; muscular area in brachial valve defined by 

 thickened rounded ridges, divided by central rounded ridge 

 extending From the bifid cardinal process, and dividing ante- 

 riorly. 



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

 only ). 

 Stropheodonta plicata. Hall. (Fig. 104.) (13th Ann. 

 Rep't X. V. State Cab. Nat. Hint... p. 90. Pal. 

 \. V.. Vol. IV.. PI. LXIII.) 



Distinguishing Characters. — Small size ; 

 strong rounded or sub-angular plications, 

 which increase in number towards the front 



Fi<;. 104. Strophe- 

 odonta pjicota in by implantation. These readilv distinguish 



tenor "t brachial .1 ~ 



nS^p'SSsfbroS this species from S: demissa. its nearest ally. 



SS&fromagut^ Foilnd only in the Demissa bed. at Section 

 percha cast. < Drigi- _ / , 



nai.i .) (not common ). 



Genus CHONETES. Fischer de Waldheim. 



[Ety. : ('hone, a funnel.] 



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

 X. V.. Vnl. VIII., Pt. L, p. 303.) 



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

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

 ox ;d: hinge 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 (del tidium). The upper margin of the area 

 bears a single row of hollow spines. Area of brachial valve 

 without spines. Cardinal process appearing quadrilobate. 

 Interior of shell strongly papillose in the pallia! region. A 

 low median ridge divides the muscular area of the pedicle 

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

 nal surface usually covered by radiating stria?. 



