Brachiopod from the Lower Helderberg group. 239 



cava Hall. Mr. J. M. Clarke has also called the writer's 

 attention to some of the peculiarities of this group, and to 

 one or more new and interesting associated species which he 

 has recently discovered, and which are congeneric. 



As the type species is among the rarer forms from the 

 Lower Helderberg strata, it is probable that lack of material 

 has prevented any one from determining its principal charac- 

 ters. Up to this time, no dorsal valve has been described or 

 illustrated, and the features of the ventral valve have not been 

 considered of sufficient moment or determination to warrant 

 a separation from Leptwna. 



The material studied by the writer comprises six specimens, 

 three of which are separate valves, one ventral and two dorsal. 

 Also, the original types in the American Museum of Natural 

 History in New York City have been examined, and it is now 

 evident that we have enough knowledge of the species to 

 remove it from jLeptc&na, and to draw some interesting com- 

 parisons with forms which hitherto have had no apparent rela- 

 tionship to it. 



Leptjenisca, gen. nov. 



Shell concavo-convex, attached to foreign objects by calcare- 

 ous cementation of the ventral beak. Yalves articulated by 

 teeth and sockets. Dorsal or socket valve (figures 4, 5) con- 

 cave ; interior with a broad, more or less defined, spiral im- 

 pression on each side of the median line, making a single 

 volution. Adductor impressions small. Cardinal line narrow, 

 bearing in the center two prominent, bilobed, cardinal pro- 

 cesses, separated to admit the vertical septum in the opposite 

 beak (figures 2, 3). 



Yentral valve (figure 1) convex, area elongate, triangular, 

 fissure covered with a pedicle-sheath. Cardinal muscular scar 

 supported on or limited by two elevated lamellae. Cavity of 

 beak divided by a vertical septum, on each side of which, in 

 the anterior half, is a small adductor scar. Shell structure 

 punctate. Type Leptcena concava Hall. 



Besides the foregoing essential characters presented by the 

 type species, there are others which are mainly of specific in- 

 terest. Both valves are strongly papillose on the interior, and 

 the dorsal has a low ridge within the margin, impressed by the 

 vascular lines. The surface ornamentation consists of fine 

 alternating interrupted radiating strias, very closely resembling 

 the sculpture of many species of Zejytwna. 



There appears to be little in common between this species 

 and Leptmna of the L. transversalis type, except in the articula- 

 tion of the valves, the punctate shell structure, and the general 



