NATURAL SCIENCES OF PIIILADELrHIA. 17 



o 



striae gradually increase in size, and become more irregular in 

 tlieir arrangement, but soon pass above into very regular larger 

 transverse lines, separated by spaces about twice as wide as the 

 lines themselves. These spaces gradual!}'' increase in breadth, 

 until the}' become five or six times as wide as the lines, above 

 which point they continue very regular in their arrangement, 

 about four of the lines and three of the intervening spaces occu- 

 pying a space of 0.10 inch. Near the smaller end, the flattened 

 spaces show what appear to be impressions of septa made visible 

 through the thin shell b}^ pressure. Two of these occup}' a space 

 of 0.10 inch. 



As it is seen flattened in the matrix, the very regular transverse 

 lines on this fossil give it somewhat the appearance of an attenu- 

 ated Conularia ; but as it shows no indications whatever of longi- 

 tudinal angles or furrows, it cannot belong to that genus, from 

 which it also diflTers in texture, though I am not quite sure that 

 it is an Orthoceras. It will be readilj' distinguished by its surface- 

 markings alone, from any species of the latter genus hitherto 

 described from our Coal-measures. In its surface-markings, it 

 bears some resemblance to Dentaliur)i cinctian, de Koninck (Am. 

 Foss. Belg., pi. xxii.. Fig. 3), which Prof, de Koninck afterwards 

 refers to the genus Orthoceras. Our shell, however, is much 

 more rapidl}' tapering, and straight instead of arched. 



Locality and position. Newark, Ohio. Lower Coal-measures. 



ILLINOIS COLLECTIONS. 



'STREPTACIS WHITFIELDI, Meek. 



Shell small, elongated, slender, and very gradually tapering ; 

 volutions nine or ten, increasing gradually and regularly in size ; 

 first or embryonic turn minute, planorbicular and standing edge 

 upward ; succeeding turns convex and obliquely coiled ; suture 

 deep and very oblique ; aperture ovate. Surface smooth. 



Length, 0.16 inch ; breadth, 0.04 inch ; slopes of spire straight, 

 with a divergence of about thirteen degrees. 



This little shell agrees so nearly with those Tertiary species on 

 which Deshayes founded his genus Aciculina, that I am strongly 



> I referred this shell to Aciculina, Desh., in MS.; but as that name was 

 I)reoccupied, I propose for our type the name Streptacis. 

 [187L 



