114 [ SENAxa 



pi. xxiii, f . 2 & 3). The general form and the finest details of the surface 

 markings are almost exactly the same : the difference is in the more 

 strongly incurved beak and area in our shell, and the finer intermediate 

 and concentric striae. Some varieties of this species show, in addition to 

 these surface markings, fine interrupted concentric wrinkles in the umbonal 

 region, which give it somewhat the character of Strophomena patersoni. 

 Geological position and locality. Limestone of the Upper Helderberg 

 group, New- York. 



Stbophomena inequiradiata. 



. Strophomena ( Strophodonta) pateesoni ( n. s.). 



Pal. N.Y. Vol. iv. 



Shell semioval : ventral valve very convex, gibbous in the 

 middle, somewhat abruptly deflected at the sides and front, 

 sometimes marked by a few radiating undulations which affect 

 both ventral and dorsal valves towards the front ; hinge-line 

 straight, often slightly salient. Surface marked by distant ele- 

 vated radiating lines ; the intermediate spaces marked by fine 

 radiating striae, and crossed by short abruptly arching wrinkles 

 which are interrupted by the strong radiating striae : finer ra- 

 diating striae, from twelve to twenty, between the stronger ones ; 

 area unknown. 



This shell varies, in the convexity of the ventral valve, from moderately 

 convex to very gibbous ; some specimens being abruptly bent or geniculate 

 towards the front. The vascular impression is bilobed, of moderate size, 

 and the cast presents a closely punctate surface. 



This species is related to Leptcena stephani^ Barrande ( Bra*ch. aus 

 Bohmen, taf 20, f. 7 ; Haidinger, Naturwissenschaftl. Abhandlungen), 

 but is never so extended in the hinge-line nor so arcuate as the represen- 

 tatives of that species ; the vascular impression is larger, and the concentric 

 wrinkles are always arched in well-preserved specimens of our species. 



