MUSEUM OF COMPARATIVE ZOOLOGY. 121 



Pleurotomella Agassizii Verrill & Smith. 



Pleurotomella Agassizii V. & S., Am. Journ. Sci., XX. p. 394, 1880; Trans. Conn. 



Acad. Sci., V. p. 454, pi. lvii. figs. 3, 3 a. 

 ? Pleurotomella Sandersoni Verrill, Trans. Conn. Acad., VI. pp. 149, 26G, pi. xxxi. 



figs. 3, 3 a, 1884. 



This remarkably fine species, peculiar in its colored columella, is ruder and 

 larger and more thick-skinned in the north ; smaller, more elegantly sculp- 

 tured, whiter, and with less epidermis in the Gulf of Mexico. This form, 

 which rarely exceeds 25 mm. in length, and has the color on the pillar very 

 faint or absent, may take the varietal name of, mexicana. After a careful com- 

 parison of the young of this species with an authentic specimen of P. San- 

 dersoni, I am much inclined to the opinion that the latter is merely a more 

 slender variety with the transverse ripples on the anal fasciole finer and more 

 numerous. I can see no other differences. The name may be retained in a 

 varietal sense. 



This form, though apparently not rare in the mainland arcbibenthal region, 

 was not obtained among the Antilles on the Blake Expedition. 



Pleurotomella Edgariana n. s. 



Plate XXXVI. Fig. 6. 



Shell large, straw-colored with a tinge of rufous about the margin of the 

 anal sulcus outside ; whorls 10-1 1 (seven remaining, nucleus and first normal 

 turn broken away) ; whorls keeled or angulated at the periphery, the keel not 

 riblike or sharp, but lightly rounded ; in the first small whorls it is undulated 

 or obscurely nodulous, but in the last four or five whorls not so ; from it the 

 posterior part of the whorl ascends to the suture almost in a straight line or 

 section of a cone, the anterior slope is full and rounded; the anal fasciole 

 is polished and marked only by the fine silky incremental strife; the other 

 transverse sculpture solely of fine incremental lines ; spiral sculpture, beside 

 the keel, of fine, rather angular threads (about seven in a space of 3.0 mm.) 

 with a single finer thread generally present, on the last whorl, in the inter- 

 spaces ; these cover the whole shell, which appears when quite perfect to 

 have a thin dark olive-colored epidermis, of which only traces remain on the 

 type ; aperture very large, the notch being one quarter of a volution in extent, 

 very wide, and gently rounded into the outer lip, which is correspondingly 

 curved forward ; canal short, wide, hardly differentiated from the aperture; 

 columella nearly straight, a broad (in the type specimen) rather thick mar- 

 ginated callus extending from in front of the notch around on the body, well 

 around behind the columella, and so on to the canal ; in the type the edge of 

 the callus is somewhat thickened and raised, but this seems to be due to senile 

 degeneration. Max. Ion. of shell (tip lost), 58.0 ; of last whorl, 45.0; of aper- 

 ture, 35.0; diameter at broken tip, 1.5; max. diameter, 25.0 nun. 



