The Rogers Gap Fauna of Central Kentucky 143. 



Shell extremely thin, of a pearly white color. The type was found 

 at the railroad cut 59.1 miles from Ludlow. 



This form evidently is closely related to Conularia trentoneusis, 

 from the Trenton of New York. In the latter species, the trans- 

 verse stride are not as narrow, so that they appear stronger, and the 

 intermediate spaces are not as wide as in the Rogers Gap form. 

 Moreover, the vertical striae are much narrower, leaving room fre- 

 quently for still finer intermediate striae, visible only under a lens. 

 The faces of the shell are more convex, and the sulci at the angles 

 are more deeply impressed. The shell substance in all specimens 

 seen is black, but this may have no significance, since the enclosing 

 rock also is black. In the Rogers Gap form, the interspaces be- 

 tween the vertical striae are too narrow to admit of intermediate 

 striae. 



42 — Orthoceras rogersensis, sp. nov. (Plate I, Figs. 17A, B) 

 — Shell increasing from 16 to 24 mm. in a length of 72 mm. This 

 is equivalent to an angle of about 6 or 7 degrees. In any part of 

 the shell, the number of chambers in a length equal to the average 

 width of the shell equals six or seven. The septa are moderately 

 concave. The siphuncle is more or less excentric. Where it 

 passes through the septum its width equals about one-tenth of the 

 width of the shell. Within the chambers the sip'huncle expands 

 at once, close to the septum, so that where the siphuncle has a diam- 

 eter of 1.5 mm. in passing through the septum, its width immedi- 

 ately within the chamber equals 2.0 mm., and toward the central 

 part of the chamber it equals about 2.75 mm., the interval between 

 the septa being 3.7 mm. This corresponds to only a moderate 

 widening of the siphuncle within the chambers as ordinarily ex- 

 posed in weathered specimens, the narrow passage through the 

 septum not being visible in such specimens. The shell is rarely 

 preserved. It is very thin and comparatively smooth. Under 

 a lens, however, both transverse and longitudinal striae may be 

 seen. Of these the longitudinal striations are low and broad, about 

 9 to 11 in a width of 5mm. The transverse striae are much nar- 

 rower, sharper, and at more irregular intervals, but also number 

 frequently 10 in a length of 5 mm. On some parts of the shell 



39 



