TRIGONUDA. 247 
situated near the cardinal line. Type, P. ventricosa, Con. (exxiv, 
98). Carboniferous; Kansas. This genus, Conrad says, bears 
the same relation to Carbonicola that Margaritana bears to Unio. 
Mr. Meek says, “1 differ from Mr. Conrad in regard to the rela- 
tions of Prisconaia; I think it belongs to the Trigoniidz, near 
Schizodus—if not the same.” 
ReEmonpDIA, Gabb, 1869. 
Distr.—R. furcata, Gabb (exxvii, 58,59). Cretaceous; Mexico. 
R. Bronnii, Krauss. Cretaceous; So. Africa. 
Shell compressed, elongately subquadrate, inequilateral, the 
beaks being subanterior; ligament very short, external; hinge 
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. 
? Iscuyrina, 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. 
Curronotvs, 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 emarginated tooth in the left valve fitting into a special 
pit of the right valve; the forms of Curtonotus are also much 
more regularly oval. 
DoraBra, 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. 
