364 MEXICAN BO VNDARY SHELLS— BALL. 



Lejytobyrsus the gyration ceased in time for the pilhir of the completed 

 shell to appear normally straight and the axis impervious. In a per- 

 fectly adult B. rameniosus the margins of the aperture are expanded 

 and slightly thickened, but not reflected. The diameter of the hollow 

 axis varies in different specimens. 



Family GLAXDIXID.E. 



Genus PSEUDOSUBULIN A, Strebel and Pfeffer. 

 PSEUDOSUBULINA EISENIANA, Cooper. 



It has already been shown by Strebel and Pfeffer (1882) that some of 

 the small Mexicau species with a shell closely resembling Stenogyra and 

 S2)iraxi,s are destitute of a jaw and have a dentition closely resembling 

 that of GUindiHa. These were separated under the name of Pscudosiib- 

 iiUna, with a longitudinally ribbed Stenogyra-\ike shell having a smooth 

 nuch^ar portion and a truncate pillar (Ex. P. chiapensis, Pfeffer). To 

 this grouj) a subgenus was added under the name of Volutaxis, distin- 

 guished by having axially ribbed nuclear whorls and the pillar not 

 truncate, but slightly thickened and twisted, and passing more or less 

 directly into the sharp edged peristome. The species described by Dr. 

 Cooper, under the provisional name of MeUinieUa {tasiensis and M. 

 eiscnuoia, the latter being sinistral), are almost exactly intermediate 

 between the typical Pseudosuhulina ami Yolutaxis, indicating that the 

 two groups should be consolidated. In these two species the nuclear 

 whorls, when perfect, are delicately axially ribbed ; the young shells have 

 a straight ])illar, not truncate, but with an angle at the base which, in 

 the adult, is more or less obsolete, while the pillar becomes not plicate, 

 but somewhat thickened. 



In P. eiseniana there is no jaw. The animal is pale colored, and was 

 so ('ontracted in the specimens that the existence of labial pulpi, of 

 which there was no evidence, could not be absolutely denied. It is> 

 however, probable that there are none. The very minute radula is of 

 the shape of the same organ in CtJandlna^ oval, with the rows of teeth 

 meeting at a sharp angle in the median line. There are about 13 

 slender, arched, needle like teeth on each side of a very small, low, 

 slender, narrow rhachidian. Some of the laterals api»eared to have a 

 double cusp, which may have been pathological; in general they resem- 

 bled the laterals of Glmidina, but had the cusps more drawn out, slen- 

 der, and relatively about twice as long compared with the base. 



Genus STREPTOSTYLA, Shuttleworth. 



STREPTOSTYLA NEBULOSA, new species. 



(Plate XXXIII, iig. 4.) 



Shell of a biilliant yellowish brown, clouded irregularly with opaque 

 blotches, thin, ovoid, with 5i whorls; nucleus smooth, the apex blunt, 



