94 University of Michigan 



The specimens from southern Aruba are quite distinct from 

 any of the other subspecies, but those from the central por- 

 tions are usually smaller, often have more distinct riblets, and 

 intergrade slightly with knipensis. The sinistral shells are 

 similar in sculpture and size to the dextral specimens from 

 Seroe Canashito (A4), but their definite distribution seems 

 to require recognition as at least an incipient local race. The 

 type locality of form sinistrorsa is the top of the low shore- 

 cliffs just south of Kralendijk (A5c). 



Brachypodella gibbonsi, new species 

 Cylindrella raveni Gibbons (1879; J. of C, I, 340); first Bonaire 

 record. 



Type locality: (B3) base of western escarpment of Mon- 

 tague, Bonaire. 



Distribution: Bonaire (B3-6, 8), Klein-Bonaire (Kl) ; un- 

 der limestone rocks. 



Shell (fig. xvii-71) : considerably smaller, more acuminate, 

 and lighter in color than raveni; greatest diameter at the 

 penultimate whorl. Whorls: 12% (in a medium-sized speci- 

 men) , of which about 8 are usually retained ; more convex and 

 with deeper sutures than raveni; last whorl relatively more 

 elongate. Growth-riblets of later whorls : much higher, heav- 

 ier, and more distant than in raveni; expanded into heavy, 

 white crests over the basal carina. Plane of aperture about 

 on a level with the periphery of the last whorl {i. e., although 

 the last whorl is equally tangential, it is not carried as far for- 

 ward as in raveni). Peristome: heavier. Embryonic whorls 

 and other characters as in raveni. 



Radula (fig. xvi-66) and jaw: very similar to raveni, but 

 the centrals are usually bicuspid although a rounded projec- 

 tion is sometimes developed in the shallower notch. 148 trans- 

 verse rows counted in a complete specimen. 



This species has more distant riblets than B. raveni sanctae- 

 harharae, while they are heavier than those of the subspecies 

 knipensis. Although this species does not intergrade with 

 either, it appears more closely related to the northern and 

 southern forms than to typical raveni of central Curasao. 



