DALL: MOLLUSCA AND BRACHIOPODA. 281 



Pleurotomella (Pleurotomella) polystephanus Dall, n. sp. 



Shell of moderate size of six or more whorls, the apex eroded, white, with a 

 cream-colored periostracum ; spiral sculpture of numerous fiue, subequal, flattish 

 threads with narrower interspaces, which cover the whole shell ; to these are added 

 a thickened ridge which borders the anterior margin of the suture, and on the spire 

 a peripheral nodose keel, which is less marked on the last whorl, where it forms 

 the shoulder ; on the penultimate whorl there are twenty of these nodules ; other 

 axial sculpture is furnished by fine, short, sharp elevated wrinkles which cross 

 retractively the ridge adjacent to the suture, like the " gathers " of a skirt, and 

 become obsolete ou the fasciole ; there are twenty-eight of these wrinkles on the 

 margin of the peuultiiuate whorl; the space above the shoulder is distinctly 

 excavated, especially on the spire ; suture distinct and, on the earlier whorls, 

 almost channelled ; aperture ovate ; anal fasciole comprised in the nodose shoulder, 

 not reaching the suture ; outer lip arcuately produced forward; pillar with a thin, 

 smooth layer of enamel, obliquely attenuated distally, somewhat twisted ; canal 

 wide, shallow. Lou. of shell, 25 ; of last whorl, 19 ; of aperture, 14.5 ; max. 

 diam. 12.5 mm. 



U. S. S. " Albatross," station 2808, near the Galapagos Islands, in 634 

 fathoms, sand, bottom temperature 40° F. U. S. N. Mus. 96,498. 



The several encircling rows of nodosities or wrinkles give this shell a particu- 

 larly elegant appearance. 



Pleurotomella (Pleiirotomella) dinora Dall, n. sp. 



Shell small, short-fusiform, stout, white with a pale yellowish periostracum, and 

 about seven whorls ; apex defective, subsequent whorls rather rapidly increasing, 

 with an appressed suture behind a smootli and constricted anal fasciole iu front of 

 which the shell is shouldered by a series of short, slightly protractive ribs, of 

 which, on the penultimate whorl there are fifteen, with subequal intersj)aces aud 

 crossed by half a dozen irregularly spaced spiral striations ; these striae are ill 

 defined, and on the last whorl extend over the base of the shell to the canal; ou 

 the last half of the last whorl the ribs become obsolete; aperture narrow, anal 

 sulcus at the suture wide and deep, the outer lip in front of it prominently arcu- 

 ate, thin and simple ; jiillar lip smooth with a thin wash of callus ; pillar twisted, 

 rapidly attenuated ; axis impervious; canal moderately wide, short and slightly re- 

 curved. Length of (decollate) five whorls, 15 ; of last whorl, 11 ; of aperture, 8 ; 

 max. diam. 7 mm. 



U. S. S. " Albatross," station 2807, near the Galapagos Islands, iu 812 fathoms, 

 ooze, bottom temperature 3S°.4 F. U. S. N. Mus. 96,479. 



This a pretty but small form, which recalls iu its general aspect several of the 

 larger Atlantic species. 



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