152 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



Vol. XXXI, 



somewhat contracted at the periphery, thus forming decidedly strongly 

 marked sutures. The whorls are crossed by numerous, quite regu- 

 larly spaced, ohliquel}" backward slanting thread like riblets, which 

 are about one-tifth as wide as the spaces which separate them. These 

 riblets are not as well developed on the middle of the spire as on the 

 anterior and posterior extremity of the shell. Antepenultimate whorl 

 decidedly less high than the preceding or succeeding volution. Base 

 and outer wall of the last whorl pinched to form a low keel at the 

 periphery, which extends l)ack from the peristome over the solute 

 portion. Anterior part of base well rounded, marked 

 b}" the strong continuation of the riblets, which pass 

 uninterrupted from periphery over the base into the 

 rather broad, open umbilicus. Parietal wall of the free 

 portion somewhat sinuous and pinched a little to the 

 loft of the junction with the outer wall. The junction 

 of the parietal and outer wall is marked by a low broad 

 keel that extends over the solute area. Junction of the 

 parietal and columellar wall angular. The entire solute 

 portion is marked 1)}^ concentric rings of riblets, which 

 become crowded behind the peristome. Aperture irreg- 

 ularly semioval, somewhat contracted in the middle of 

 the outer and parietal wall, having the posterior lateral 

 angle decidedly rounded and forming almost a right 

 angle at the junction 

 of the parietal and 

 columellar walls, well 

 rounded, and some- 

 what effuse anteriorh", 

 white. Peristome ex- 

 panded and slightly reflected. Inter- 

 nal colunm slender, very thin, trans- 

 lucent, showing many oblique white 

 lines of growth and bearing a low 

 keeKor swelling, which is located a 

 little posterior to the middle in each 

 w^horl. In the last three turns this 

 keel is replaced by a very strong- 

 lamella, which attains its maxinmm development in the middle and 

 gradually decreases in size posteriorly and anteriorly, the attenuated 

 extremity })eing visible deeply within the aperture on the columellar 

 wall. The greatest width of the lamella is equal to about one-half 

 of the diameter of the whorl and its greatest thickness to a little 

 more than one-fourth of the height of the chamber. In the last three 

 whorls, coextensive with the columellar fold, there is a spiral line 

 af slender, sharp, regularly spaced, forward and outward curved 



Fig. 11.— Ixtekiok 

 view of holo- 

 spira rosei. 



Detail ok interior of Hulospira 



ROSEI. 



