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262 Cincinnati Society of Natural History. 
vex at the upper part where they form a flattened angular ridge, which 
is continued as the form of the succeeding two radial plates and the 
secondary radials as far as preserved in our specimen. This ridge bi- 
furcates toward the subradials below. The second radials are quad- 
rangular or pentagonal and much wider than high. The third radials 
are pentagonal or hexagonal, and about as wide as high. Only two or 
three of the secondary radials are preserved in our specimen. 
The first regular interradials are nearly as large as the first radials, 
octagonal, protuberant, and presenting inclined faces toward each of 
the adjoining sutures. These are followed by two smaller interradials, 
and these again by two, beyond which our specimen is not preserved. 
A single intersecondary plate is preserved in our specimen. 
The protuberant plates and numerous cut faces will alone distinguish 
this species from any hitherto described. 
The species is founded upon a single specimen from the collection of 
W.C. Egan, Esq., in whose honor I have proposed the specific name. 
It was found in the Niagara Group at Bridgeport, in Chicago, Illinois. 
LEPERDITIA CACIGENA, 0. Sp. 
(Plate VI., figs. 5 and 5a, views magnified about five diameters. These two magnified 
illustrations are not exactly correct, but near enough for all practical purposes. They 
were drawn without the aid of photographs.) 
® 
Length usually about 12-100 inch, breadth about 8-100 inch. and 
thickness about 4-100 inch. 
General form subovate. Hinge line straight, a little more than half 
the length of the valves. Anterior end narrower than the posterior, 
extending but little beyond the hinge line, when it rapidly curves into 
the ventral line below. The posterior part is broadly rounded, and 
constitutes beyond the hinge-line full one third the length of the valves. 
Valves most convex at the posterior third. Surface smooth and eye- 
tubercle obsolete. : 
This is a true Leperditia, as one valve overlaps the other. - 
The author collected this species in the upper part of the Hudson 
River Group at Versailles, and near Osgood, Indiana. The specimens 
illustrated and described are in his collection. 
