TRIGONIID^. 247 



situated near the cardinal line. Type, P. ventricosa^ Con. (exxiv, 

 98). Carboniferous ; Kansas. This genus, Conrad saj's, bears 

 the same relation to Carbonicola that Margaritana bears to Unio. 

 Mr. Meek sa^^s, " 1 differ from Mr. Conrad in regard to the rela- 

 tions of Prisconaia ; I think it belongs to the Trigoniidae, near 

 Schizodus — if not the same." 



ReiMOndia, Gabb, 1869. 



Distr. — B. furcata, Gabb (cxxvii, 58, 59). Cretaceous ; Mexico. 

 B. Bro7i7in, Krauss. Cretaceous ; So. Africa. 



Shell compressed, elongately subquadrate, inequilateral, the 

 beaks being subanterior ; ligament \ery short, external ; hino-e 

 composed of three moderately diverging, elongated cardinal 

 teeth and one long posterior lateral in the left valve ; those of 

 the right would appear to be similar and corresponding to those 

 of the left. The middle cardinal of the left valve is transversely 

 striated, as in Trigonia, and is slightly grooved on its face ; the 

 anterior is linear and smooth, and the posterior is also smooth 

 at least on its posterior face. In the right valve the anterior 

 tooth is as large as the middle, the posterior is linear. 



?IscHYRiNA, Billings, 1866. 



Distr. — Fossil, 2 sp. Silurian ; Anticosti. I. Winchelli 

 Billings. 



Shell equivalve, inequilateral, two strong ridges radiating from 

 the beak in the interior of each valve. 



CuRTONOTUS, Salter, 1863. 



Distr. — Fossil, 6 sp. Devonian ; Britain. C. elongatus, Salter 

 (cxxv, 24). 



Shell elongately ovate ; having a thickened hinge-plate, with a 

 single strong triangular central tooth on each valve. Right 

 valve plate with an obscure tooth behind the central one. 

 Anterior muscular scar deep ; pallial impression entire. 



It seems very closely allied to Schizodus, but has not the broad 

 median emai'ginated tooth in the left valve fitting into a special 

 pit of the right valve ; the forms of Curtonotus are also much 

 more regularly oval. 



DoLABRA, M'Coy, 1844. 



Distr. — D. corrugata^ M'Coy. Carboniferous ; Ireland. 



Shell ovate or trapezoid, gibbose, with a more or less straight 

 hinge-margin, inequilateral, inequivalve, the left valve being 

 larger than the right, hinge posteriorly with an elongated tooth 

 sometimes bifid in the left valve. • 



