xxiv SYNOPSIS OF GENERA. 



strong angiilivr 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 striae, 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 

 iKJtween 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 : Gonioph(,ra perangulata, pi. xxxiv, figs. 1-6. 

 Goniophora Glaucus, pi. xliv, figs. 10-17. 



• M«Miinin< (lool. Snrv. Gt. Britain, vol. 2, pt. 1, ]>. 2(54. •* If, as I suppose, Cypricardia cymhifor-iiiix be 

 dintinct, generically, and include species of tlie mountain limestone, the name Qoniophora seems suitable. 

 It ia, however, doubtless, a mytiloid shell." 



