MUSEUM OF COMPARATIVE ZOOLOGY. 75 



Monosquillo. Station 2601, in 107 fms., sand, off Hatteras, N. Carolina, dead 

 and worn. 



This species is one of the most remarkable and elegant of any from the 

 deeper waters. It belongs to the group of which P. speciosa Reeve forms a 

 member, by its sculpture, though whether the nucleus would agree with that 

 species is uncertain. At present our judgment on such subdivisions as Gemmula 

 Weinkauff, founded on nuclear characters, must be held suspended; so far as 

 our knowledge goes, nuclear characters have little absolute systematic value in 

 this group, and their relative value remains to be determined. 



Subgenus LETJCOSYRINX Dall. 



Shell white or pale without color pattern; thin; the anal notch behind the 

 periphery or at the suture ; sculpture delicate, of spiral keels or threads and 

 often oblique riblets on the shoulder of the whorls; peripheral keel if pres- 

 ent not recurved; operculum thin, nucleus apical, scar of attachment small; 

 larval shell glassy, rounded or keeled ; other shell characters as in Plcurotoma. 

 Type Pleurotomella Verrillii Dall. 



This group is intended to contain the operculated species of Pleurotomida 

 which are so characteristic of the archibenthal region. They are distinctly 

 contrasted with the coarse, spotted or maculated shallow-water species of Pleu- 

 roma proper, by their thin, white, delicately sculptured shells ; they are apart 

 from Drillia by having no subtubular projection of the anal notch when adult 

 and no thick varix to mark their maturity; they are separable from the archi- 

 benthal Drillias also by their larger shells, longer canal, and more inflated 

 habit. The anal notch is generally wider, more rounded and nearer the suture 

 than in the typical Pleurotoma, and the operculum proportionally wider and 

 more delicate. 



Leucosyrinx Verrillii Dall. 



Plate X. Fig. 5. 



Pleurotoma (Pleurotomella) Verrillii Dall, Bull. M. C. Z., IX. p. 57, August, 1881. 



Habitat. Station 41, 860 fms. ; Station 173, living in 734 fins., ooze, off 

 Guadalupe, bottom temperature 40° F. ; Station 46, latitude 25° 43' N., longi- 

 tude 84° 47' W., in the Gulf of Mexico, in 888 fms., ooze. Also at U. S. Fish 

 Commission Stations 2623 a, 2626, and 2628, 25 to 100 miles off Cape Fear, 

 North Carolina, in 150 to 528 fms., ooze, temperature 39° to 45° F. ; Stations 

 2677 and 2678, off Cape Fear, in 478 and 731 fms., ooze, temperature about 39° ; 

 and Station 2384, in 940 fms., mud, Gulf of Mexico, between the Mississippi 

 delta and Cedar Keys. 



This fine species appears not to have been found by the Challenger, or north 

 of Cape Hatteras. It is distinguished among several allied forms by the dis- 

 tinct fine even threads on the fasciole, the form and number of its riblets, and 

 the absence of any pre-sutural wrinkles or coronating band. 



