104 University of Michigan 



Cerion uva arubanum, new subspecies 



Cerion uva Smith (1898; Proc. Mai. Soc, III, 114); the first Aruba 

 record; collected by Hartert. 



Type locality: (A2c) Baranca Alto, Aruba. 



Distribution : Aruba ; living shells only found in a colony at 

 the type locality and in another just north of Perkietenboseh 

 (A2c, A5a) ; subfossil throughout the limestone portions of 

 the island. Similar in habits to uva. 322 adults collected. 



Although considerable individual variation (Plate XX) 

 occurs, the last whorl near the aperture tends to jut out tan- 

 gentially in this subspecies, so that the palatal wall of the 

 peristome usually projects out from the preceding whorls 

 to a greater extent than in C. uva uva and knipensis. As a 

 result of this, the umbilicus is usually larger and more open 

 in the specimens from Aruba. In making the measurements 

 of the major diameter in the two subspecies from CuraQao, 

 the calipers seldom touched the aperture, while in C. uva aru- 

 banum, the palatal wall almost always interfered. In all cases, 

 the major diameter was taken exclusive of the aperture, so 

 the true greatest width of C. uva arubanum is slightly larger 

 than the data in Table XIV would indicate. In other par- 

 ticulars, this form is similar to the smaller and more slender 

 lots of C. uva uva, although the whorls tend to be slightly 

 lower than in any of the Curagao lots except those from 

 station C13. 



The peculiar restriction of the living cerions on Aruba to 

 two isolated colonies is very puzzling, especially since this 

 species very evidently was almost universally distributed on 

 the island in former times. Subfossil shells occur almost 

 everj-where on the limestone, and also are cemented into blocks 

 of phosphate near Culebra (Al). It does not seem possible 

 that this former distribution has been reduced by the extensive 

 cultivation of aloes, as living shells actually occur on 'his plant 

 in station A4c, while they are absent from the large, limestone 

 plateaus east of Savaneta and Sint Nieolaas, and these hills 

 appear to be mainly undisturbed by man. Although Aruba 

 has a more arid climate than the other islands and appears 



