GUELPH FAUNA. IN THE STATE OF NEW YORK 63 



and gives the shell the aspect of a true Cyclonema, (2) the deep suture, 

 with broadly excavated outer slope, (3) the differentials of the surface 

 sculpture, which over the body or outer convexity of the whorl consists of 

 fine, subequal, elevated, revolving lines, increasing by intercalation. Near 

 the suture two of these are stronger and wide apart, and on the umbilical 

 surface four are specially emphasized, being larger and more distant than 

 any of the rest. In all, the mature shell carries 20 to 25 revolving lines, 

 which are crossed by fine, crowded and rather indistinct concentric growth 

 lines, most palpable on the final whorl. The final whorl is apparently 

 slightly detached at the aperture as in P. s c a m n a t a, but the aperture 

 itself is not well retained in any of our specimens. 



There is certainly very little difference in the characters of this species 

 as we now apprehend it and the shell figured by Hall as Trochonema 

 (Pleurotomaria) pauper from the Racine limestone at Racine. 

 There is a striking discrepancy between the description of that species and 

 its illustration which may be due wholly to the fact that the drawing was 

 made from material not accessible when the description was printed. S. A. 

 Miller, 1 for reasons not evident, has ranked this species as a synonym for 

 Pleurotomaria halei Hall, but this is unquestionably erroneous. 



Notwithstanding the resemblance of this shell to Cyclonema, we find 

 that it is kept from that association by the presence of a deep though nar- 

 row umbilicus, and perhaps also by the coexistence of opercula which 

 Whiteaves has discovered but which have not yet been recorded as occurring 

 in Cyclonema. The apparent detachment of the final whorl at the aperture 

 and the loose coiling evinced by the very deep suture in all these shells 

 constitute another difference from Cyclonema in which the whorls distinctly 

 embrace each other. 



1 Cat. Paleozoic Fossils, p. 422. 



