258 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
Borsonta Bellardi, 1838. Shell fusiform, with spiral and axial sculpture, the 
anal suleus close to the suture, wide and shallow ; the canal elongated, the pillar 
with a single plait (or, according to Cossmann, in the type species two) on the 
proximal part of the pillar. Type B. prima Bellardi. 
The abyssal and Pacific Coast species are sufficiently different and numerous to 
stand as a distinct group from that containing the Italian fossils, as follows : 
BonsowELLA Dall, nov., 1908. Shell with a small, blunt nucleus of one or 
two whorls, sculpture chiefly spiral, feeble, except for one or two spiral carinae, 
sometimes with a few small riblets or beads on the principal carina; periostracum 
conspicuous, smooth or vermiculate ; canal wide and very short; outer lip sharp, 
simple, arcuate; pillar solid, with one strong, nearly horizontal plait continuous 
upon the whole axis; axis impervious, operculum absent. Type Borsonia dalli 
Arnold. 
There is never more than one plait in Borsonella; in Cordieria, as restricted by 
Cossmann, there are never less than two. In Rouaultia the anal sulcus is narrow, 
sharp, and situated at the shoulder in the peripheral carina. Both Cordieria and 
typical Borsonia have a long and slender canal and the general aspect of Gem- 
mula, while Borsonella resembles an Antiplanes with a strong plait on the 
proximal part of the pillar. 
GywNoBELA Verrill, 1884. Shell ample, stout, smaller than the average 
Pleurotomella, with a short spire and no operculum. Type G. curta Verrill. 
"These shells occupy, so far as the shell characters are concerned, a place in the 
Mangilinae analogous to that which is assigned to Bela among the operculate 
forms. 
PLEUROTOMELLA Verrill, 1873. Shell with a small blunt nucleus of several 
whorls, closely arcuately axially ribbed, the succeeding whorls with axial and 
spiral sculpture, short-fusiform ; the anal sulcus close to the suture, deep and 
wide, with a distinct fasciole; canal very short, narrow, recurved ; outer lip thin, 
. simple, sharp; pillar thin, gyrate, anteriorly obliquely truncate, almost pervious. 
Animal blind, inoperculate. Type P. packardii Verrill. 
The original type was a small, very delicate shell, but species subsequently 
added to the group attain a notable size and solidity. 
Puvwonurwonus Dall, 1908, nov. Shell thin, smooth, or spirally sculptured, 
axial sculpture less conspicuous ; fusiform, canal nearly obsolete, pillar and outer 
lip simple; sulcus wide, shallow, close to the suture; animal blind, with a dis- 
tinct muzzle into which the proboscis is retracted, operculum wanting, Type 
Pleurotomella castanea Dall, 
The average Pleurotomoid gastropod, as far as indicated by the animals figured 
and those examined by the writer, has a simple orifice under and covered by the 
head and expanded tentacular bases; in the species of the present section a pro- 
jecting flat-ended muzzle exists, which permanently extends beyond the line 
joining the tentacles, and into an aperture in the end of which the proboscis is 
