124 AMERICAN JOURNAL 



In P. violacea there are three angular (including post- and 

 pre-angular) digitations as in P. miUipeda, and instead of one 

 median fascicle there are two. Digitations (S, 1. A. l-fl+l. (!•) 

 P. M. 1. (I.) (A. M. 1 (I). P. l.)=10. 



3. Aperture. 



Two quite different forms of aperture are recognizable in the 

 Lamarckian genus. In P. lambis, &c,, the aperture is linear, 

 about equally wide from front to rear, and almost coequal in 

 length with the whorl, and the cavity of a large tubercle which 

 generally exists in the angular fasciole is open to view ; a trans- 

 verse fold is, however, on the columella behind and combines 

 with a similar one generally developed on the opposite lip, be- 

 hind or in front of the cavity, to form a constriction between 

 the aperture proper and a canal emptying into the posterior or 

 marginal digitation. All the species resembling P. lamhis in 

 the number and distribution of the primary spines agree likewise 

 in the form of aperture. 



P. cliiragra and P. rugosa have an unguiform or claw-shaped 

 aperture, but little curved, and the region of the angular tuber- 

 cle and cavity is concealed by the contraction of the aperture, 

 produced by longitudinal plication of the columella and a corres- 

 ponding development of the labral surface. 



4. Character of lip surface. 



The species of the group exhibit much difference in the char- 

 acter of the surface of the lips, some having a very smooth and 

 polished callous surface, while in others the surface is much 

 wrinkled and folded. They may be considered in order of de- 

 velopment. 



1st. In P. lamhis P. hryonia and P. crocata, the lips are 

 covered with a perfectly smooth callous coat. 



2d. In P. chiragra the margins of the aperture are delicately 

 wrinkled, the wrinkles being white. 



3d. In P. violacea the surface of the outer lip is delicately 

 wrinkled, while the rugae of the inner are still fainter. 



4th. In P. millipeda the wrinkles are about equally devel- 

 oped on the surface of both lips, but they are comparatively little 

 raised. 



5th. In P. Scorpio, P. pseudoseorpio and P. elongata as well as 

 P. rugosa, the wrinkles are very prominent, and pearly white, 

 strongly contrasting with the purple intervals. 



§ 2. Taxonomic Deductions. 

 Having thus examined the modifications of the principal dif 

 ferential characters which distinguish the species of Pterocera, 



