132 AMERICAN JOURNAL 



SPECIES. 



Eight distinctly marked species are distinguishable among the 

 forms that have been described or indicated. These may be 

 naturally grouped with reference to the development of certain 

 •characters. Of primary importance seems to be the condition of 

 labial surface, some being smooth and others rugose at that re- 

 gion ; those having rugose lips differ again in the development of 

 the processes between the primary labral spines, such processes 

 being generally simple lobes in some species, while in others 

 they are extended into involute spines. The general form, orna- 

 mentation, development of the lip, and especially of the spines, 

 in their respective variations furnish other excellent characters 

 for the discrimination of the species. As several important dif- 

 ferences seem to have hitherto been generally overlooked, the 

 following synopsis and amended but incomplete diagnoses of the 

 species may be acceptable : 



Synopsis. 



I. Lips smooth. 



la. Body whorl tuberculated at the angle. 

 Lip eflected ; columella with callus diffused, P. lamhis. 

 Lip inflected; columella with callus stratified, P. crocata. 



lb. Body whorl unarmed at angle, P. bryonia. 



II. Lips rugose. 



Ila. Intercalary digitations none. 

 Posterior digitation with a basal lobe, P. scorpms. 



Posterior digitation simple, P. 2:>seudoscorpio. 



lib. Intercalary digitations developed. 

 Posterior digitation simple, P. ynillipeda. . 



Posterior digitation with a basal lobe. 



Labral digitations 8 ; labral wrinkles very 



distinct, P. elongata. 



Labral digitations 10 ; labral wrinkles 



faint, P. violacea. 



A. Aperture smooth within. Primary digitations of 

 labrum only developed ; six, or exceptionally seven 

 in number.* 



1. P. LAMBis, Lam. ex Linn. 



Stromhus lamhis, Linn., Syst. Nat. ed. 12, p. 1208. 

 Pterocere scorpion, Blainv., Malac. pi. 25, f. 3, 4. (not Lam.) 



*In a specimen of P. bryonia in the collection of the Smithsonian In- 

 stitution, there are four angular spines, the lower of which is forked, as 

 in an example mentioned by Humphrey. 



