CYRTINA OF THE HAMILTON .GROUP. 
269 
deltidium. These features are shown in the casts and in transvers sections 
of the valve. The dorsal valve shows a double or bilobed cardinal process, 
with the strong crural bases supporting spiral arms, which are directed 
into the two compartments of the ventral valve, and, making numerous 
turns, terminate in the rostral part of the shell. 
I have heretofore compared this species with Cyrtina heteroclita ( = Calceola 
heteroclita , Defrance; $ 'pirifera heteroclita, Yon Bitch, &c.); but in that one the 
plications are described as angular, and generally less numerous than in ours; 
though the variety multiflicata, Davidson, has more numerous plications; and 
this, with other characters, shows that the fossil undergoes variations similar to 
our own, and that it is a closely allied form holding a similar geological position. 
The specimens in the Hamilton group of New-York are usually small, measuring 
about half an inch in length and breadth; the largest one seen by me being a little 
more than fb of an inch in width, and about in length from the apex to the 
front of the valve. In some Canadian specimens, the length and widtli are about 
of an inch. The species has a wide geographical and considerable vertical range; 
being known in the Schoharie grit (Plate xxvii, f. 1, 2 & 13), Corniferous lime¬ 
stone, Hamilton and Chemung groups.' 
Figures 3 and 4 of Plate xxvii are.from the Corniferous limestone of New 
York. 
I am indebted to Dr. James Knapp of Louisville, Kentucky, for the specimen illustrating 
the spires, which is figured on Plate xliv, fig. 50. This one is from the Corniferous lime¬ 
stone, and presents six or seven turns of the spire ; while some specimens from the Hamilton 
group have shown, on being cut through, ten or eleven turns of the spire. 
The figures 26 - 33, Plate' xliv, present the usual aspect of the species in the Hamilton 
group in New-York, while 37 - 40 are of a larger individual. 
Figures 34 - 36 are of a variety where the area is flat, and the plications more angular 
than usual. 
Figures 41 & 42 are of a large individual from the Hamilton shales of Canada West. 
Figure 51 is of a specimen of this species from the Hamilton group of Iowa, received from 
Mr. 0. St.John ; and I have similar forms from near Iowa city. 
The transverse and. longitudinal sections, showing the interior structure, are of speci¬ 
mens from the Hamilton shales of Canada West. j 
Geological formations and localities. This species occurs in the Schoharie grit, 
in Albany and Schoharie counties, and in the Corniferous limestone- of. Eastern 
and Central New-York, and at St.Marys and Cayuga in Canada West. In the Ha¬ 
milton group, it occurs on the shores of Cayuga, Seneca and Canandaigua lakes, 
at Moscow, York, Darien, Hamburgh and Eighteen-mile creek in New-York; near 
Cumberland in Maryland; abundantly at Widder station in Canada West; at 
Independence, Rockford and Waterloo in Iowa. 
n tke Chemung group, the var. recto.occurs at Philipsburgh in Allegany co. 
