10 PROCEEDIlSrGS OF THE NATIONAL MUSEUM vol. 70 



fleeted. The internal pillar very broad in the antepenultimate whorl 

 and the one preceding it, narrowing posteriorly and anteriorly. In 

 the last portion of the penultimate whorl the parietal fold begins to 

 make its appearance and extends posteriorly for two turns, reaching 

 its maximum development in the antepenultimate turn where also 

 the parietal fold is present, strongly developed, and decidedly out- 

 curved at its free margin. The basal fold here also is strongly de- 

 veloped as is the labial fold. 



The type (Cat. No. 363140 U.S.N.M.) was collected by C. R. Or- 

 cutt at Monterey, Nueva Leon, Mexico. It has 15.3 whorls and meas- 

 ures — length, 16 mm. ; diameter, 4.3 mm. 



Cat. No. 363141 U.S.N.M. contains 31 topotypes, which yield the 

 following measurements, and a number of fragments: 



Greatest. 



Least 



Average . 



Number of 

 whorls 



16.2 

 11.1 

 14.2 



Length 



20.3 



12.1 

 15.9 



Diameter 



4.5 

 4.0 

 4.4 



HOLOSPIRA (HOLOSPIRA) MITRAENSIS, new species 



Plate 1, fig. 9 



Shell cylindroid, white. The, type, the only specimen before us. 

 consists of almost the last five whorls. It is sufficiently peculiar 

 to merit description. Whorls moderately rounded, marked by obso- 

 lete axial riblets which are a little more strongly developed on the 

 last whorl than on the earlier ones, but even here they are very poorly 

 expressed. Suture moderately constricted. Periphery well rounded. 

 Base short, very strongly rounded, narrowly openly umbilicated, 

 marked by the continuation of the axial riblets. The last whorl is 

 solute and is marked by moderately closely spaced, rather irregular 

 axial threads which encircle the whorls. There is also a strong angle 

 present on this portion behind the posterior angle of the aperture 

 and a less pronounced angle behind the junction of the columella 

 and parietal wall. Aperture rather large, with a strongly expanded 

 and reflected peristome. The internal axis is hollow, very narrow 

 in the last whorl, and a little less so in the penultimate. A slender 

 columnellar fold begins in the penultimate whorl and extends 

 through the two whorls preceding this, reaching its highest deA^elop- 

 ment in the fourth to last turn where also the parietal and basal 

 lamellae, which are almost confined to this turn, attain their highest 

 development. Here, too, the slender labial fold is present. 



The type (Cat. No. 363142 U.S.N.M.) was collected by C. R. 

 Orcutt at La Mitra Mountain, Monterey, Nueva Leon, Mexico. 

 Length, 8.9 mm.; diameter, 3 mm. 



