328 PAL^ONTOLOGr OF NEW YORK. 



GeiNTS CfflLOSPIRA (Hall). 



I'he species published under the name of Leptocadia concava in the third 

 volume of the Palaeontology of New York, page 245, was subsequently 

 found to possess internal spires, arranged in a somewhat peculiar manner, 

 and connected by a strong loop. This feature rendered it necessary to 

 remove the fossil from the association in which I had placed it, w^ith Lepto- 

 calia imbricata and L. fldbellites, and I have proposed for it the generic name 



CCELOSPIRA.* 



This genus differs but little from Zygospira proposed by me in 1862,f and 

 it may be found desirable to unite the two under that designation, extending 

 the characters so as to include the types of both the genera ; but this can 

 only be done after the discovery and examination of other species which 

 may serve to unite the forms already described. 



The shells of C(elospira are concavo-convex, having the ventral valve 

 convex or sometimes subangularly arching over the concave dorsal valve. 

 The surface of the shell is striated or plicated, with the plications simple 

 or bifurcating, and of which two or more in the centre of the ventral valve 

 are more conspicuous than the others, forming a more or less defined mesial 

 fold; upon the dorsal valve there is a corresponding depression. The 

 space between the valves leaves little room for the spires, and these append- 

 ages appear to be somewhat loosely arranged, with their apices approaching 

 each other. These shells are apparently fibrous in texture ; and on this 

 account, and from the position of the spires, they approach more nearly to 

 Atrypa than to Trematospira, to the latter of which they are more nearly 

 allied in external form. 



The Terebratula harrandi of the Wenlock limestone of England belongs appa- 

 rently to the genus, being closely allied to O. disparilis (= Atrypa disparilis) of 

 the Niagara group (Palaeontology of New York, Vol. ii, p. 277), holding likewise 

 a similar geological position. 



• Sixteenth Report on the State Cabinet, p. 60. 1863. 

 t Fifteenth Report on the State Cabinet, p. 154. 1862. 



