160 PALEONTOLOGY OF NEW YORK. 



are crossed by traces of the radial surface plications. Between them lie the 

 narrow obovate adductor scars. 



In the brachial valve the beak is inconspicuous; the umbonal region de- 

 pressed for about one-third the length of the shell, thence anteriorly becoming 

 developed into a median fold. The greatest convexity of the valve is attained 

 in front of the center. The cardinal margin is scarcely thickened ; the dental 

 sockets quite narrow. The hinge-plate consists of two Hattened processes, in- 

 clined toward each other and closely approximate along their inner bases, 

 though not meeting. Each process is divided into an anterior and posterior 

 lobe, the latter being the smaller and resting upon the former. These an- 

 terior lobes are narrow and slender, and constitute the crural bases. Spirals 

 are present, but their direction and the nature of the loop are undetermined. 

 A stout median ridge supports the hinge-plate and divides the scars of the 

 adductor muscles. In both valves the lateral portions of the umbonal region 

 is pitted. The plications of the surface are covered by fine, sharp and ele- 

 vated concentric strite. Shell substance, fibrous, impunctate. 



Type, Clintonella vagabunda, sp. nov. Clinton group. 



Observations. This interesting shell possesses a hinge-plate of similar struc- 

 ture to that prevailing among the spire-bearing genera of the Clinton fauna, 

 Whitfieldella {W. intermedia, W. naviformis), Hyattella (H. congesta, H. junia), 

 CoELOSPiRA {C. planoconvexa), and occurring also in the genus Zygospira. 

 Though the structure of its brachial supports is unknown, the association of 

 the hinge-plate and the peculiar muscular impressions, with the strongly plicated 

 rhynchonelloid exterior, would effect an incongruity if introduced into any of 

 the generic divisions now recognized. The evidence now attainable indicates 

 an intimate relation to Zygospira, and from these indications it seems probable 

 that this shell will be found to possess introverted spirals. 



Clintonella vagabunda was obtained from a drifted and decomposed block ol 

 sandstone found without label among the collections presented to the New 

 York State Museum by the Albany Institute. This specimen had been collected 

 by the late Governor De Witt Clinton, in remembrance of whose intelligent. 



