806 Report or THE State Gxroxoaist. 
Nucleospira, Hall. 1859. 
(Plate 38, figs. 21-38.) 
Shells usually small; subcircular in outline. Valves sub- 
equally convex, often gibbous or ventricose. Hinge-line 
very short, cardinal extremities rounded. On the pedicle- 
valve the cardinal area is low and obscured by the incurvature 
of the beak. Only in very young specimens is the deltidium 
Fic. 380. Fic. 381. 
Fia. 382. Fia. 383. 
Fic. 880.—A preparation of Nucleospira ventricosa, Hall; showing the umbonal blades, the 
jugum and the form of the first volution of the spirals. 
Fras. 381, 382.— The primary lamellz and jugum of Nucleospira ventricosa, Hall. 
Fia, 383.— A preparation of Nucleospira concinna, Hall; showing one-half of the brachidium, 
the mode of attachment of the crura to the umbonal blades and the flattened 
stem of the jugum. 
exposed, and it then consists of two plates attached to the lateral 
margins of the delthyrium; in mature individuals these plates 
are coalesced and incurved, the median suture is lost and the 
foramen covered; the appearance of the deltidium is that of a 
triangular concave plate, limited by rather sharp dental ridges 
and covering the delthyrium for about half its length. The 
teeth are prominent, approximate, recurved at the tips, supported 
by thickened bases but not by lamellew. Dental sockets very 
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