1899.] NATURAL SCIENCES OF PHILADELPHIA. 187 



IX, figs. 1, 2), as the original figures given by Bland and repro- 

 duced by Binney are rather crude. This specimen measures, alt., 

 1.58; greatest diameter, 2.62; lesser diam,, 2.4 mm., almost 

 exactly the same as P. arctica. It has fully 5^ whorls. 



Whether the lip-rib will prove a constant character of P. Lan- 

 singi, and constantly wanting in P. arctica, can only be decided by 

 larger series than have yet been collected; but the slightly greater 

 number of whorls of Lansincji in a shell of the. same size, with the 

 higher position of the periphery, apparently indicate that P. arctica 

 is specifically distinct, and unless specimens of intermediate charac- 

 ters come to light, it must stand as a species. 



Prof. William H. Dall tells me that he collected arctica at Coal 

 Harbor in the Shumagin islands, and it was taken by Turner at 

 Unalashka. He believes it may prove to be a flat-topped species 

 of Conulus. 



The species of Pristiloma now known may be recognized by the 

 following key: 



a. — Shell sculptured with radial grooves above; lip simple and 



acute. 



b. — Grooves crowded, not very deep; spire conic; whorls 



about 7; diam, 3 or 4 mm. . , P. Stearnsi (Bid.). 



b' — Grooves deep, separated, the whorls with a corona of low 



tubercles; whorls 5i; diam. 2.56 mm. P. Pilsbryi Van. 



a'. — Shell nearly smooth throughout. 



b. — Aperture broadly lunate; no lip -callus; spire narrow, 

 almost flat; whorls 4, the last wide; diameter more 

 than double the altitude; diam. 2.5, alt. 1.1 mm., 



P. TayloriVAs. 



b'. — Aperture narrowly crescentic; spire low-conic; whorls 



regularly widening; diameter less than double the 



altitude. 



c. — A denticulate lip-rib within the margin of the outer 



lip; periphery above the middle; whorls 5|-; alt. 



1.58, diam. 2.62 mm. . . P. Lausingi (Bid.). 



e'. — Xo lip-rib; periphery submedian ; whorls 4f ; alt. 1.58, 



diam. 2.66 mm P. arctica (Lehn.). 



