GESUS LEPTOCCELIA. 365 



OeI^LTS LePTOCCILIA (Hall). 



This name was proposed in the Tenth Report on the State Cabinet 

 (1856, published 1857), for some forms usually referred to Terebratula 

 and Rhynchonella by authors. The genus was described and illustrated 

 in the Twelfth Report on the State Cabinet, 1859.* 



I have subsequently found it necessary to separate some of the species 

 originally included under this genus, on account of a different internal 

 structure ; but the typical forms remain as first characterized. Unfortu- 

 nately the specimens 'have not yet yielded a full knowledge of their 

 interior structure. 



Lept()C€plia acatiplicata. 



PLATE LVII. 



Jltrypa aculiplicata : Coskad, Annual Report on the Paleontology of New-York, p. 54. 1841. 



This species is described by Mr. Conrad as follows : " Short, ovate 

 " acute, compressed, with six to eight acute profound plicae ; beak of 

 " larger valve acute, concave beneath the apex in front ; three or four 

 " strongly marked concentric impressed lines. Locality : Near Water- 

 " ville, in Onondaga limestone." 



The shell is plano-convex, varying in form from ovate acute to orbi- 

 cular. The ventral valve is moderately convex, with the beak slightly 

 incurved. The dorsal valve is depressed-convex, sometimes flat or con- 

 cave from compression. 



In the greater number of specimens, the plications are from six to 

 eight on each valve, strongly angular ; the central one on the ventral 

 valve depressed, and margined on each side by a larger one, while on 

 the dorsal valve two plications are slightly elevated, giving an abrupt 

 sinuosity in front. The shell is concentrically marked by strong imbri- 

 cating lines of growth. 



• Sec Twelfth Report on the State Cabinet, p. 32 ; and Palaeontology of New- York, Vol. iii, pp. 245 

 and 447. 



