6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 79 



lated by the ribs. On the first and second of the remaining turns 

 strong, distantly spaced, decidedly retractively slanting axial ribs are 

 present. On the following turns these ribs become sigmoid, a little 

 less strongly developed, and much more closely approximated. The 

 intercostal spaces on the first and second turns are broad, and are 

 marked by two spiral cords a little stronger than the rest at the 

 angulation. The shoulder between this angulation and the summit 

 on the first and second turn is crossed by about 10 slender spiral 

 threads, while the space between the suture and the strong thread 

 anterior to it at the angulation is marked by 5 spiral threads, which 

 are considerably stronger than those on the summit. On the three 

 remaining turns the stronger threads corresponding to the angula- 

 tion in the middle of the turn become reduced, and only equal those 

 anterior to it in strength. There are 10 of these subequal threads 

 present, while the 10 slender threads on the posterior portion of the 

 turn remain feeble. On the next postnuclear whorl this differentia- 

 tion of spiral sculpture almost disappears, and we find 14 equal and 

 almost equally spaced, rather strong spiral threads and a few feeble 

 incised lines near the summit present between the summit and suture. 

 On the last whorl 16 subequal and subequally spaced spiral threads 

 are present between periphery and summit. Here the deeply im- 

 pressed pits between the ribs and the spiral threads show finely 

 incised spiral lines. Base slightly produced, marked by a continua- 

 tion of the axial ribs, which become evanescent on the anterior por- 

 tion of the base, and by 13 strong spiral threads, of which those on 

 the posterior portion of the short columella are a little heavier than 

 those posterior to it. Anterior to these strong threads there is a 

 series of six spiral threads that are much finer and much more 

 closely appoximated than those posterior to it. These are closely 

 crowded at the extreme anterior tip of the columella. Aperture 

 rather large, auriculate; the sinus at the posterior angle very pro- 

 nounced, less channeled anteriorly. Outer lip abruptly expanded, 

 very much thickened and separated by a varix a little posterior to 

 its edge. The inner edge of the callus becomes somewhat attenuated 

 near the posterior angle, and the attenuation is sufficiently abrupt 

 to give it a somewhat toothed aspect. The columella is reflected as 

 a moderateh^ broad callus and the parietal wall is covered by a strong 

 thick callus which joins the outer lip at the posterior angle. 



r^jpe.— U.S.N.M. No. 368132, collected by C. D. Alleman on 

 Taboga Island, Panama. It has 5.1 whorls remaining, and meas- 

 ures : Length, 7.4 mm. ; diameter, 3.2 mm. 



Remarks. — The species, while suggesting Rissoina zcltrwri De 

 Folin, which also comes from Panama, is nevertheless quite different 

 in sculpture and in general form and the shape of the early whoris, 

 and the strong sculpture differentiates it from all other species. 



