184 



I>istin^u;uisliiu<j; CharHctcrs. — Sub-circu- 

 hu- or oblate outline; greater tran8^'erse 

 diameter; convex brachial valve, with 

 a[)ex near the margin ; flat or concave 

 pedicle valve with large oval pedicle 

 groove; and fine concentric striae, with 

 Jr^\ "seveSi'^lt^hed occasionallv coarser wrinklcs. 

 shells (from Hall). Fonnd ill tlic middle Moscow (Orljicu- 



loidea ) l»ed. at Sections 4 and 5. 



Orbiciloidea LODiK.Nsis. Vaiuixem. (Fig. 84.) (Pal. 

 N. Y., Vol. IV., p. 22, PL II.) 



Distin^^iiisliing ChnvHrters. — I>i-oadly oval-ovate ontline ; 

 narrower posterior end; low brachial \alve, with minnte 

 eccentric ajjcx ; linear j^edicle groove extending 

 more than half way from apex to margin in 

 ])edicle valve; concentric stri<e, and faint radiat- 

 ing folds or nndnlations on the anterior half of 



Fig. 84. Orbicu- tllC sliell. 

 loidea lodiensis. i i n • 



Brachial valve, Foniid \\\ tiic Dcmissa bed, at Section 5; the 



Demissa bed, x ' ■ 



2%. toriginai.) Plenrodictvnm bed. at Wanakah Cliff; the 

 Nantilns bed, in Avery's Ravine. It is rare in all. 



Measurements : G mm. b}' 5 mm. in length and width. 



Gems SC^HIZOBOLUS. Ulrkh. 



[Ety. : Schtza, a cleft ; oholxs, a geuus.] 



(1886: Contributions to American Palaeontology, Vol. I., p. 23, Pi. III. 

 Pal. N. Y., Vol. YIII., Pt. L, p. 87.) 



Shell oval, valves slightly iine(jnal, margins thickened ; 

 pedicle valve with a notch in the posterior margin ; shell 

 substance largely corneous. Muscular callosities of pedicle 

 valve on each side of a median ridge with narrow curved 

 lateral scars, bi-achial valve without tlie scars, but with 

 thickened band just within posterior margin. 



ScHizoBOUS TRUNCATrs. Hall. ( Fig. 85. ) (Discina trun- 

 cata. Hall. Pal. X. Y., Vol. IV.. p. 23. I^ls. I. and II.) 



Distinguishing Characters. — Abruptly rounded or trun- 

 cate posterior margin ; ajnces of both valves near posterior 



