386 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 83 



tion of the axial riblets and spiral threads, those on the posterior 

 half of the base being finely spinose and those on the anterior half 

 and within the umbilicus finely scalloped. Aperture broadly oval: 

 peristome double, the outer very broadly expanded, tinted and 

 marked with closely spaced lamellae; inner peristome slightly ex- 

 serted and reflected, appressed to the outer. Operculum thin, pauci- 

 spiral, with submarginal nucleus covered by a granular calcareous 

 deposit. 



The type, U.S.X.M. no. 567755, has a little more than 4 whorls 

 remaining and measures: Length, 16.8 mm: greater diameter, 12.2 

 mm ; lesser diameter, 7.5 mm. 



This species, like C. {€.) irmdimhs. is lively and readily comes 

 from the shell when it is permitted to remain quiet for a little while. 



This species was collected by Portuando and later by Bartsch on 

 two small limestone blocks lying off the north side of El Palenque 

 near the house of Desidero Sanchez. 



This species has the combined characteristics of C. (C.) pt^esasia- 

 num and C. {C.) irradiaihs. It is possible that it may represent a 

 hybridization of the two. However, all of our specimens are so uni- 

 form in their characters that if hybridization is their source then 

 fixation has taken place. 



CHONDROPOMA (CHONDROPOMARTES) IRRADIANS (Shuttleworth) Pfeiffer 



Shell elongate-conic, varj'ing in ground color from white to pale 

 horn-color to pale brown. The postnuclear whorls are marked with 

 interrupted spiral bands of brown of varying width, which are also 

 arranged in axial series, the bands on the spire being a little broader 

 than those on the base. Interior of aperture of the same color as 

 the outside. Peristome white, with broad brown rays. There is an 

 oblique brownish band marking the plug at the truncated end. 

 Nuclear whorls 2.3, strongly rounded, smooth with a few incremental 

 lines at the termination of the nuclear spire; the whorls remaining 

 well rounded, narrowly shouldered at the summit, marked by feeble, 

 retractively slanting, moderately closely spaced axial and spiral 

 threads, the latter a little stronger than the axial. The junctions of 

 these two elements form feeble nodules, while the spaces enclosed 

 between them are more or less squarish pits. The spiral threads 

 near the summit show more of a tendency toward nodulation than 

 those on the middle of the turns. Periphery of the last turn well 

 rounded. Base short, well rounded, marked by the continuation of 

 the feeble axial and spiral threads. The latter are here of about 

 the same strength as those on the spire, but rendered a little more 

 strongly nodulose by tlie axial threads than on the spire. The base 



