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 flattened 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 striae. 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. jmia), 
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. 
