WEST AMERICAN PYRAMIDELLID MOLLUSKS. 145 



mate turn. The junctions of the ribs and spiral cords form moder- 

 ately strong tubercles, while the spaces inclosed between them appear 

 as almost circular, well-impressed pits. Periphery of the last w^horl 

 marked by a spiral keel a little less strong than those between the 

 sutures. Base well rounded, somewhat attenuated anteriorly; 

 marked by five almost equal and equally spaced spiral cords and 

 two very slender lirations, the latter near the columella. The deep 

 grooves between the spiral cords are marked by numerous slender 

 axial lirations. Sutures subchanneled. Aperture irregular, some- 

 what channeled anteriorly. Posterior angle obtuse, outer lip thin, 

 rendered sinuous by the spiral cords. Columella slender, sigmoid, 

 reenforced by the base, provided with a strong, deep-seated fold at 

 its insertion. Parietal wall covered with a famt callus. 



Prof. C. B. Adams's type is at Amherst College, and was collected 

 in the Bay of Panama. It has eight post-nuclear whorls and meas- 

 ures: Length 3.3 mm., diameter 0.9 mm. 



ODOSTOMIA (CHRYSALLIDA) CLATHRATULA C. B. Adams. 



Plate 14, figs. 7, 7a. 



Chemnitzia clathmtula C. B. Adams, Ann. Lye. Nat. Hist. N. Y., vol. 5, 1852, 

 pp. 389, 390. 



Shell elongate-conic, slender, vitreous. Nuclear whorls two and 

 one-half, forming a depressed helicoid spire, whose axis is almost at 

 right angles to that of the succeeding turns, in the first of which it is 

 about one-half immersed. Post-nuclear whorls very slightly rounded, 

 strongly constricted at the sutures and prominently shouldered at 

 the summit, marked by well rounded, tuberculate, axial ribs, of 

 which 14 occur upon the first and second, 16 upon the third, 18 upon 

 the fourth and fifth, and 24 upon the penultimate turn. In addition 

 to the axial ribs, the whorls are marked between the sutures b}^ four 

 spiral cords which equal the ribs in strength, and render them tubercu- 

 late at their j unction. Sutures broadly and deeply channeled. Periph- 

 ery and the somewhat prolonged base of the last whorl well rounded, 

 the latter marked by seven narrow, almost equal, and equally spaced 

 spiral keels, the broad space between which and the peripheral sulcus 

 are marked by many slender axial riblets. Aperture oval ; outer lip 

 (fractured anteriorly) thin, showing the external sculpture within; 

 columella stout, slightly curved, strongly reflected over the reenforcing 

 base, provided with a strong fold at its insertion. 



Professor Adams states that ten specimens in various stages of 

 growth were collected in the sand of the Bay of Panama; two of 

 these are in the collection at Amherst College. 



We have figured the better of the two individuals which has seven 

 post-nuclear whorls and measures: Length 2.8 mm., diameter 0.9 mm. 



