OF COXCHOLOGY. 121 



the presence of only five ; tracing those digitations to their origin, 

 it is further found that a still more important distinction pre- 

 vails, and that they are very difi'erently grouped and developed 

 from entirely different elements. 



In the one group, that embracing the largest number of spe- 

 cies, — those having six digitations, and of which P. lamhis is a 

 representative, — the distribution is as follows : 



1st. Just below the suture is a fasciole, (s^Uural), but little 

 differentiated, which finally trends upwards on the spire, and ter- 

 minates in a single digitation accumbent on the spire, and con- 

 tinued more or less upwards from its apex. 2d. Between the 

 suture and angle, in the mature shell, a fasciole becomes de- 

 veloped which emits a spine (post angular) directed backwards. 

 3d. Around the angle of the cone is a fasciole {angular) gene- 

 rally indistinct, but becoming well developed a short distance 

 from the lip in the adult, and terminating in a digitation. 4th. 

 Below or in advance, another fasciole [pre-angular) crirds the 

 whorl, and also terminates in a digitation ; the distinction between 

 the third and fourth is generally slight, and the angular tuber- 

 cles covering both in common, tliey may perhaps be considered 

 as forming a compound fasciole. 5th. Another fasciole (metZ/a?) 

 girds the whorl around the mjddle and likeAvise terminates in 

 a digitation. 6th. Still another [jMst-sinual) emits a spine be- 

 hind the sinus ; an antesinual fasciole is unarmed ; as is also a 

 lobal. The canal terminates in a long tortuous digitation curved 

 toAvards the right. Finally, reference must not be omitted to an 

 auriform lobe with which the posterior digitation is sometimes 

 furnished towards the left. 



In the second group, represented by P. chiragra, a very dif- 

 ferent distribution prevails. 1st. The sutural fasciole is repre- 

 sented by two diverging branches, one of which (sutural) con- 

 tinuing its quasi-sutural course, terminates in a spine which at 

 base crosses the spire, and is curved towards the left and up- 

 wards, and the other [sub-sutural) terminates in a spine pointed 

 backwards : 2d, the angular fasciole is undivided, and terminates 

 in a single spine, curved outwards and backwards; 3d, the 

 medial fasciole is also simple, and terminates in a single recurved 

 spine ; 4th, the postsinual fasciole Is simple, and edigitate ; 5th, 

 the ante-sinual fasciole is well developed, and the lobal terminates 

 in a large recurved spine ; the siphonal canal is cornuform and 

 recurved towards the left. 



As to the homologies between the digitations of the species of 

 this group and those of the preceding, there can be no doubt, 

 after due study. 



The large posterior digitation recurved to the left represents 



