38 PROCEEDINGS OF THE NATIONAL MUSEUM. vou 49. 



c^. Axial sculpture not couBisting of ribs only. 

 d^. Axial sculgture consisting of ribs and fine raised threads 

 between them. 



e ^ Whorls decidedly inflated baheri, p. 56. 



e^. Whorls not inflated. 



f\ Axial threads between the ribs fine woodwardii, p. 57. 



/^. Axial threads between the ribs coarse newcombii, p. 58. 



d^. Axial sculpture consisting of ribs but no fine threads be- 

 tween them ; sculpture between the ribs consisting of 



irregular crinkly markings cleo, p. 58. 



b^. Axial sculpture consisting of obsolete ribs. 



c '. Shell elongate-ovate cerrosensis, p. 59. 



c^. Shell not elongate-ovate but elongate-conic. 



d^. Shell slender, ribs faint, adult shell 2.8 mm dalli, p. 59. 



d^. Shell stout; ribs more strongly developed, adult shell 



3.5 mm coronadoensis, p. 60. 



DESCRIPTION OF SPECIES. 



RISSOINA FIRMATA C. B. Adams. 



Plate 32, figs. 4, 6. 



Rissoa Jirmata C. B. Adams, Ann. Lye. Nat. Hist. N. Y., vol. 5, 1852, p. 401. 

 Rissoa scalariformis C. B. Adams, Ann. Lye. Nat. Hist. N. Y., vol. 5, 1852, p. 402. 



Shell of medium size, white, semi translucent. Nuclear whorls 

 decollated, a portion of the last turn only remaining. The succeeding 

 turns are well rounded, decidedly appressed at the summit with some- 

 what of a shoulder, which extends over the posterior third of the spaces 

 between the sutures. The whorls are marked with exceedingly strong, 

 decidedly protractively curved sublamellar axial ribs, which are some- 

 what irregularly spaced. Twelve of the ribs occur upon the first and 

 14 upon the remaining turns. The intercostal spaces are at least four 

 times as broad as the ribs and are crossed by very slender, closely 

 spaced, quite evenly developed spiral tlu-eads, which pass up on the 

 sides of the ribs, but do not appear to cross their summit. Of these 

 spiral threads, about 40 occur between the sutures on the antepenid- 

 timate turn. Sutures well impressed, rendered sinuous by the strong 

 ribs. Periphery well rounded. Base moderately long, marked by 

 the strong continuation of the axial ribs, which extends to the umbil- 

 ical space, intercostal spaces sculptured, like those of the spire. Aper- 

 ture moderately large, broadly oval; posterior angle neither acute nor 

 obtuse; outer lip very thick at the edge. Columella short, very stout, 

 curved, reflected over and appressed to the base as a thick callus; 

 parietal wall covered with a thick callus, which fuses with the outer 

 lip and the columella. 



Professor Adams's type was found in sand at Panama. It has 7 

 postnuclear whorls and measures: Ijength, 4.7 mm.; diameter, 2 mm. 



Professor Adams's Rissoa scalariformis, of which he collected a 

 single specimen at Panama, proves to be the young of the present 



