SYNOPSIS OF GENERA. xlix 



basal extremity ; post-cardinal slope often with an obscure or more or less 

 defined fold along the middle of its area. 



Surface marked by more or less regular, fine concentric striiB of growth. 



Hinge-line (in the cast) marked by a groove indicating a strong lateral tooth 

 or fold. There is likewise a groove along the hinge-line anterior to the beak 

 and a divergent furrow extending toward the anterior margin. Ligament 

 external. Muscular impressions and pallial line undetermined. 



The species of this genus constitute a remarkable group of inequivalve shells. 

 Their geological position is in the upper part of the Chemung group, and the 

 only others which might be considered as having relations with them are the 

 Palseanatinae, which are similar in their inequivalve character. 



The hinge characters cannot be fully determined, but the remarkable feature 

 of a cardinal line extending the entire length of the shell with a longitudinal 

 fold, which seems scarcely to be interrupted at the beaks, together with the 

 diverging anterior process or clavicle, are characteristic and peculiar features. 



Examples : Prorhynchus quadratum, pi. Ixxix, figs. 40-49 ; pi. xcvi, fig. 5. 

 Prorhynchus nasutum, pi. xcvi, fig. 6. 

 Prorhynchus angulaium, pi. xcvi, fig. 7. 



Glossites, N. GEN. [Type, Glossites lingualis, Hall.] 



Shell equivalve, inequilateral, narrowly or broadly elliptical in outline. An- 

 terior end short, margin declining from the beak and curving below. Posterior 

 end large, narrowly or broadly rounded at the extremity. Beaks small and ap- 

 pressed, sub-anterior, or in advance of the anterior third. Cardinal line long, 

 gently arcuate. Umbonal slope not defined, prominent above and usually 

 merging into the general convexity of the surface about the middle of the length. 



Surface marked by fine concentric striae of growth, which are often raised 

 into sharp sub-lamellose elevations, or more rarely by stronger concentric ridges. 

 Obscure radiating striae are rarely observed. 



Hinge characters undetermined. There is evidence of an elongate lateral 

 tooth or fold, and the valves are joined by a strong external ligament. Lunule 

 distinct. Muscular impressions shallow. 



