CYRTINA OF THE HAMILTON GROUP. S69 



deltidium. These features are shown in the casts and in transvers sections 

 <tf 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, Defr<\xce; Spinfera heteroclita, Von Buch, &c.); l)ut in that one the 

 plications are described as angular, and generally less numerous than in ours; 

 though the variety multipUcata, Davidson, has more numerous plications; and 

 this, with other characters, shows that the fossil undergoes valuations 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 W of an inch in width, and about yi in length from the apex to the 

 ^ front of the valve. In some Canadian specimens, the length and width are about 

 ^ of an inch. The species has a wide geographical and considerable vertical range; 

 being known in the Schoharie grit (Plate xxvn, f. 1, 2 & 13), Corniferous lime- 

 stone, Hamilton and Chemung groups. 



Figures 3 and 4 of Plate xxvn 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. StJohn ; 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. 



Geological fornuitions 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 Widdcr station in Canada West ; at 

 Independence, Kockford and Waterloo in Iowa. 



I u the Chemung group, the var. recta occurs at Philipsburgh in Allegany co. 



