NO. 1903. WEST AMERICAN PYRAMIDELLID MOLLUSKS—BARTSCH. 2Y5 



nodulose on the early whorls; the fourth, or suprasutural one being 

 smooth. On the last whorl the nodules are obsolete. Of these 

 cords, the one at the summit is the weakest and the second below 

 it the stronojest. The spaces between the spiral keels are about half 

 as wide as the keels and rather shallow. In addition to the spiral 

 sculpture the whorls are marked by slender, almost axial riblets, 

 which render the three posterior keels on the early whorls nodulose 

 at their intersections. Of these riblets, about 18 occur upon the 

 second and 22 upon the third whorl. On the fourth, which is the 

 penultimate, the p;rooves between the keels are crossed by slender 

 axial threads. Sutures strono;ly constricted. Perii)hery of the last 

 whorl marked by a narrow, deep sulcus. Base moderately long, 

 well rounded, marked by five spiral cords which grow successively 

 weaker between the i)eriphcry and the umbiUcal area. Grooves be- 

 tween the sutural cords equal, crossed by numerous, slender, axial 

 threads, which cause the spaces between the threads and cords to 

 appear as minute pits. Aperture moderately large, somewhat effuse 

 anteriorly; posterior angle acute; outer lip thin, showing the external 

 sculpture withm; inner lip moderately long, strong, somewhat 

 curved, and reflected over and adnata to the base, provided with a 

 slender fold at its insertion; parietal wall covered with a thin callus. 



The type (Cat. No. 211 62, U.S.N.M.), which was collected by 

 Mr. Kelse}'" at San Diego, California, has 5 post-nuclear whorls and 

 mea.surcs: Length, 3 mm.; diameter, 1.5 mm. 



This species follows Odostomia (Chrysallida) lielga in the key. 



ODOSTOMIA (CHRYSALLIDA) THALIA, new species. 

 Plate 36, fig. 3. 



Shell small, elongate-ovate, bluish- white, semitranslucent. Nu- 

 clear whorls obliquely immersed in the first of the succeeding turns, 

 above which half of tlie tilted edge of the last volution only projects. 

 Post-nuclear whorls well rounded, feebly shouldered at the summit, 

 marked by very slender, poorly developed, decidedly retractive, 

 axial ribs, of which about 30 occur between the sutures upon the last 

 two volutions. In addition to these axial ribs, the whorls are marked 

 by low, feebly rounded, rather broad spiral cords, of which 6 occur 

 between the sutures, on the second, and 7 upon the third and fourtJi 

 whorl; the spaces separating the spiral cords are narrow, impressed 

 lines. The intersections of the axial ribs and spiral cords form weak 

 tubercles, whUe the spaces inclosed between them are roundish pits. 

 Sutures moderately constricted. Periphery of the last whorl well 

 rounded, marked by a cord equaUing the one posterior to it in \\^dth, 

 and separated from that by a line as wide as tliose on the spire. Base 

 moderately prolonged, well rounded, marked with 12 low, rounded 

 spiral cords, which decrease successively in width from the periphery, 



