UROCOPTW MOLLUSKS—BARTSCH. ' 127 



HOLOSPIRA (HOLOSPIRA) MEXICANA, new species. 



Plate IV, fig. 9. 



Shell suhcylindric, Avith gradually tapering- teriiiinul cone, yellowish 

 horn color, with irregularly distributed whitish areas, resembling 

 frosting. Nuclear whorls two and one-half, the second one inflated, 

 all very finely granulose. Post-nuclear whorls quite well rounded, 

 the greatest convexity falling a little posterior to the middle between 

 sutures. The last three or four whorls are somewhat contracted 

 anteriorly. The whorls are marked by irregular and irregularly 

 spaced, ill-defined riblets, which are best developed on the early 

 whorls and the last half of the last volution. On the fifth w^horl there 

 are about 56 of these slender, oliliquely backward slanting threads, 

 while the tenth shows no less than 80. On the penultinate whorl 

 the riblets number 48, but are almost obsolete. Periphery and 

 base of the last whorl w^ell rounded, crossed by the ri])lets which 

 continue into the small perforate umbilicus. The last two milli- 

 meters of the last wdiorl are solute and built out. There is a 

 well-marked angle extending over the solute portion, at the junc- 

 tion of the parietal wall and the columellar margin. The outer 

 surface of the solute portion is marked by quite strong riblets, which 

 form concentric rings, and these are more closely crowded immedi- 

 diately l)ehind the peristome than farther back. Peristome decidedly 

 expanded but not reflected (accidentally bifid in the posterior lateral 

 margin in the type), white-edged, fading gradually to light brown 

 within. Folds not apparent in the aperture. Internal pillar thin, 

 polished, hollow throughout, of almost uniform diameter posterior to 

 the thirteenth whorl,- where it is equal to about one-sixth the diameter 

 of the shell, tapering gently anteriorly from the thirteenth whorl, 

 marked by many irregularl}^ spaced, obliquely backward-curved 

 whitish lines. A low, obsolete, somewhat submedian twist extends 

 over the entire pillar. In the antepenultimate and the whorl preced- 

 ing this, the axis bears a strong lamella, which attains its maximum 

 development in the whorl preceding the antepenultimate, beyond which 

 it extends only a half of a turn posteriorly; anteriorly the fold 

 diminishes gradually till it disappears in the penultimate whorl. 

 In the whorl preceding the antepenultimate, a strong, somewhat out- 

 ward-curved spiral lamella hangs from the middle of the roof and 

 extends about halfway down across the chamber, while a strong, low, 

 spiral lamella is raised up from the middle of the floor, leaving onW 

 the space of about one-third of the height of the chamber open 

 between these two lamelke. On the inside of the outer lip of the 

 same whorl there is a low spiral keel, which is opposite the open 

 space between the two spiral lamelhx; just described, that is, a little 

 posterior to the junction of the floor and outer wall. 

 Proc. N, M. vol. xxxi— 06 9 



