206 
PALEONTOLOGY OF NEW YORK. 
faunas of the Lower Helderberg and Oriskany groups. Eatonia bears very 
much the same relation to Uncinulus as the subgenus Pugnax to the cuboidal 
shells of Hypothyris. The species of Eatonia possess two quite distinct types 
of exterior, one strongly plicated over fold, sinus and lateral slopes, the other 
radially lineate, with broad margins of contact, which are usually crenulated as 
if by the extremities of the rounded plications. To the former belong E. medi- 
alis, Vanuxem, and E. eminens, Hall, of the Lower Helderberg group, E. sinuata 
and E. Whitjieldi, Hall, of the Oriskany sandstone; to the latter, E. singularis, 
Vanuxem, of the Lower Helderberg, E. peculimis, Conrad, of that fauna and of 
the Oriskany sandstone, and E. pumila. Hall, also of the Oriskany sandstone. 
Genus CYCLORHINA, gen. nov. 
plate lxi. 
1860. Rhyncliospira, Hall. Thirteenth Kept. N. Y. State Cab. Nat. Hist., p. 83. 
1867. Trematospira?, Hall. Palaeontology of New York, vol. iv, p. 412, pi. Ixiii, figs. 33-36. 
1889. Retzia {Trematospira), Wuitbaves. Contrib. Canadian Palseont., vol. i, pt. 2, p. 116. 
Shells of comparatively large size at maturity, subtriangular in outline; 
biconvex, the convexity of the brachial valve being the greater. Fold and 
sinus very broad, and developed in the usual manner, on brachial and pedicle- 
valves respectively. 
On the pedicle-valve the apex is obtuse, not elevated, and is very broadly 
truncated by a large circular foramen, which, even in the earliest growth-stages 
observed, is enclosed for fully five-sixths of its periphery by the substance of 
the valve. The deltidial plates are incipient at maturity and scarcely evident 
in young shells; the delthyrial margins are extremely divergent. The cardinal 
line is short but straight, and its extremities are produced on each side to form 
a short alate process or wing, similar to those in the genus Eumetria. These 
extensions occur on both valves, and are very apparent in the younger shells, 
but become somewhat obscured with the increase of convexity accompanying 
maturity. On the interior, the teeth are large and blunt, and attached to the 
lateral walls of the shell, though they also rest upon the thick lamellae similarly 
attached except at their anterior margins, and which converge downward to 
