176 PROCEEDINGS OF THE ACADEMY OF 



PLEUROTOMAEIA TEXTILIGERA, Meek. 



Shell attaining a medium or somewhat larger size, turbinate or 

 rhombic, suboval in general outline, with height a little greater 

 than the breadth; spire depressed conical; volutions four or five, 

 flattened exactly on a line with the slope of the spire from the apex 

 to near the middle of the last turn, where there is more or less 

 defined angle; last turn large, somewhat ventricose below the 

 angle, and produced so as to make this angle near the middle of 

 the entire bulk of the shell ; umbilical region a little excavated, 

 the excavation apparently being continued as a small perforation 

 up into the axis ; aperture, as inferred from sections of the body 

 volution, obliquely rhombic-oval ; suture merely linear, or some- 

 times very narrowly channelled between the middle volutions; 

 spiral band occupying, and slightly truncating, the angle of the 

 body volution, where it is flat or a little concave, and passing 

 around immediately^ above the suture on the volutions of the 

 sphere, excepting on some of the upper turns, where it seems to 

 sink nearly or quite below the suture line. Surface very neatly 

 cancellated by distinct, regular, curved, threadlike transverse and 

 revolving lines, of about equal size and distance apart, the former 

 becoming much finer and arched backward in crossing the band. 



Height of a large specimen, 1.42 inches ; breadth of revolving 

 band on body volution, 0.10 inch; angle of spire, 10° to 80°. 



I was for some time inclined to think this might be the form 

 described by Dr. White and Mr. Whitfield, from the same horizon 

 at Burlington, Iowa, under the name Pleiwotomaria Mississipi- 

 ensis, but on comparison with a sketch of the t3'pical specimen 

 in the Museum of the University of Michigan, sent to me by Prof. 

 Winchell, I find it to be quite distinct. Thet37Je specimens of P. 

 31ississi2nensis are natural casts, but Prof. Winchell's sketches 

 show that they differ from casts of the species under considera- 

 tion, in having the angle of the body volution continued on those 

 of the spire distinctly above the suture, so as to give them a tur- 

 reted appearance instead of being all flattened exactly on a line 

 with the slope of the spire. It also has the spire more elevated 

 than that of our shell, and the upper slope of the body volution 

 concave instead of flat. Indeed, White and Whitfield's species is 

 more nearly allied to P. tabulata of Conrad, from the Coal-mea- 

 sures, than it is to that under consideration. 



[August 15, 



