192 BULLETIN 192, UNITED STATES NATIONAL MUSEUM 



U.S.N.M. No. 391463 contains 191 topotypes from the same source. 



U.S.N.M. No. 391185 contains 38 specimens, indistinguishable from 

 material from the type locality, which were collected on Big Iguana Cay, 

 Comete, East Caicos, July 28, 1930, by Bartsch. 



CHONDBOPOaiA (CHONDROPS) BACONI CAICOSENSE, new subspecies 



Plate 33, Figure 3 



Of this race I obtained thousands of specimens on the rocky hill on 

 the south side of the salt lagoon on Lightborn Creek, Grand Caicos, 

 July 26, 1930. 



This differs from the other two subspecies in having the nodulations 

 at the summit very feebly developed ; in the axial threading it resembles 

 Chondropoma (Chon-drops) baconi baconi. 



The type (U.S.N.M. No. 469147) has 4.3 whorls remaining and 

 measures: Length, 8.0 mm.; greater diameter, 5.0 mm.; lesser diame- 

 ter, 4.3 mm. 



U.S.N.M. No. 391 129 contains 4082 topotypes from the same source. 



U.S.N.M. No. 391359 contains a dead specimen collected by Bartsch 

 on the east side of Little Halfway Creek, Grand Caicos. 



CHONDROPOMA (CHONDROPS) BIFOBME Pfeiffer 



1858. Chondropoma hiforme Pfeiffer, Malakozool. Blatter, vol. 5, pp. 143, 1+4. 

 The truncated shell varies from pupoid to subcylindric ; the color 

 ranges from white through flesh-color to horn-color to pale brown to 

 dark brown; it may be unicolor, interruptedly banded, or marked with 

 a broad peripheral zone of chestnut-brown; aperture always pale. Nu- 

 clear whorls almost 2, inflated, strongly rounded, minutely granulose, 

 forming a mammillated, almost truncated apex. The whorl immediately 

 succeeding the nuclear turn is marked by closely spaced, hairlike, 

 slightly retractively curved axial riblets, which in turn are succeeded by 

 the postnuclear sculpture. This varies materially in the different races. 

 In all the races the axial sculpture forms slender, slightly retractively 

 curved riblets, which are gathered at irregular intervals into tufts at 

 the summit. The spiral sculpture is fairly constant and consists of strong 

 rounded cords, not keels, as in some of the other species of Chondrops. 

 The junction of the axial and spiral elements forms feeble nodules hav- 

 ing their long axis parallel with the axial sculpture. Suture moderately 

 constricted. Periphery well rounded. The base is moderately long, well 

 rounded, and marked like the spire, narrowly openly umbilicated. Aper- 

 ture broadly oval. Peristome double, forming a slight auricle at the 

 posterior angle. The inner adnate to the outer. Operculum typically chon- 

 dropsid. 



This species is found in the various keys of the Turks Island group 

 and extends over the eastern part of the Caicos group into Little In- 

 agua and Booby Cay of the Mariguana group. It breaks up into a 

 number of recognizable races, which are here described. The accompany- 

 ing key will help to differentiate them : 



