XXIV 
SYNOPSIS OF GENERA. 
strong angular ridge to the [post-inferior margin. The valves are crossed 
obliquely, sometimes vertically, by a broad undefined sinus extending from 
anterior to the beaks to the basal margin, which is usually slightly constricted 
at this point. 
Surface marked by more or less regular concentric strife, which may be either 
simple throughout or fasciculate on the anterior portion of the shell. Some 
species are marked by strong radiating striae upon that portion of the valves 
between the umbonal ridge and the sinus. 
Hinge furnished with a strong oblique fold or tooth in the left valve, situated 
just beneath the beak, and a corresponding depression in the right valve. No 
lateral teeth have been observed. Ligament external, strong ; its attachment 
to the shell is marked by one or more defined grooves. Muscular impressions, 
two; the anterior one deep and strongly marked, situated a little anterior to the 
beak and just within the anterior margin. Pallial line simple, continuing nearly 
parallel to the basal margin until it crosses the umbonal ridge, and recurving 
to the posterior muscular impression which is large and shallow, and situated 
on the posterior cardinal slope sometimes near the middle of the length of the 
shell. 
This genus was proposed by Phillips * in 1848 as a generic designation for 
the original Cypricardia cymbiformis of Sowerby, but without generic definition 
or illustration of internal characters, and so far as known, the genus has never 
been heretofore described. 
The shells here referred to Goniophora have similar internal characters with 
Modiomorpha , the external form and especially the strong umbonal ridge being 
the principal distinguishing features. This generic form occurs in the Trenton 
limestone, Niagara group, Schoharie grit, Hamilton and Chemung groups. 
Examples : Goniophora perangulata, pi. xxxiv, figs. 1-6. 
Goniophora Glaucus, pi. xliv, figs. 10-17. 
* Memoirs Geol. Surv. Gt. Britain, vol. 2, pt. 1, p. 264. " If, as I suppose, Cypricardia cymbiformis be 
distinct, generically, and include species of the mountain limestone, the name Goniophora seems suitable. 
It is, however, doubtless, a mytiloid shell.” 
