174 



[Senate 



COLPOCERAS. (new genus.) 



Or. xoXtcos, sinus, and xfpa^, coi'nu, in allusion to the deep sinus in the 

 septa. ' 



Cylindrical or sub-cylindrical, septa oblique to the axis of the shell, 

 regularly arched on the dorsal side, and bending downwards in a deep 

 sinus towards the mouth on the ventral side. 



COLPOCERAS VIRGATUM. 

 Plate 5, flg. 2. 



Tube virgate, scarcely diminishing towards the apex j surface strong- 

 ly annulated ; annulations arching towards the apex on the back of the 

 shell and bending downwards in an abrupt sinus on the ventral side, 

 and becoming almost entirely lost on the ventral line ; septa following 

 the direction of the annulations and arranged between them, except on 

 the ventral side where they encroach a little upon the annulation, being 

 more abruptly bent downwards ; septa in the longitudinal section, cut- 

 ting each side, regularly arched ; section when not compressed cylin- 

 drical ; siphuncle unknown ; character of the surface, except the annu- 

 lations, unknown. 



This species occurs near the junction of the Birdseyeand Black river 

 limestones in Le\^is county. 



ASAPHUS EXTANS. 

 Plate 3, fig. 1. 



Reference. — jfsapkus extans. Palaeontology of New-York, vol. i., 

 page 228, plate 60, fig. 2, a, b, c. 



This species, which was described as an asaphus, with some doubt, 

 has again fallen under my observation, and though the specimens yet 

 procured are fragments, they throw some farther light upon the 

 character of the fossil. These specimens are mostly in a bad state 

 of preservation, from a dark shaly layer near the base of the Trenton 

 limestone in Lowville. The character of the caudal shield which is 

 preserved in several specimens is well marked, though the rings of the 

 thorax attached aie so much obliterated as to afford very little satisfac- 

 tory evidence of their number or character. Still there appears to be 

 nine or ten articulations of the thorax, though the junction with the 

 caudal shield is obscure. 



In connexion with a mutilated specimen, we have the convex middle 

 lobe of the cephalic shield, with two large and prominent eyes. This 



