146 
PALAEONTOLOGY OF NEW YORK. 
anterior instead of posterior bend at its junction with the lateral branches, and 
each of these branches bears a single row of irregular, somewhat ramose pro¬ 
cesses directed toward the inner edges of the umbonal blades. What the sig¬ 
nificance of these processes may be is not evident from a study of the specimen. 
They do not appear to be of mechanical origin or due to crystallization of silica 
upon the lamellse, but may possibly indicate a pathological or excresential 
condition. 
Fig. 132. 
l.oop of Nucleospira, sp. ?, from the Corniferous limestone at the Falls of the Ohio. (c.) 
Genus CYCLOSPIRA, gen. nov. 
PLATE LVv LlV 
1842. Orthis, Emmons. Geology of New York; Kept. Second Dist., p. 395, fig. 4. 
1847. Atrypa, Hall. Palaeontology of New York, vol. i, p. 139, pi. xxxiii, figs. 3 a-e. 
This proposed division is founded on the species, Orthis hisulcata, Emmons 
{Atrypa bisulcata, Hall), of the Trenton limestone, which in external characters 
is very similar to the Dayia navicula, Sowerby, of the Wenlock fauna. It is 
indeed surprising to find that two species so nearly alike externally, should 
differ so essentially in internal features asxto require their separation into 
groups which appear but remotely related. 
Atrypa bisulcata is a subtrihedral shell with a very convex pedicle-valve and 
a depressed brachial valve. The larger valve has a prominent umbo, the 
beak being closely incurved over the hinge, concealing both foramen and 
deltidium. The umbo is longitudinally keeled, but at about one-third the 
