THE NAUTILUS. 
17 
PEROSTYLUS, A NEW GENUS OF FUSOID GASTROPOD. 
BY H. A. PILSBRY. 
In volume IX of the Manual of Conchology, Mr. Tryon described 
and figured a shell from Port Darwin, N. Australia, as Gerithium 
( Colina ) Brazieri. Having occasion recently to study a large 
number of C. macrostoma Hinds, the type of the subgenus Colina, I 
was at once struck by the notable difference between this species and 
C. Brazieri. The latter does not seem to belong to the Cerithiidce 
at all, much less to the group Colina. I am more inclined to view 
it as an aberrant type of the Fusidce, although only a knowledge of 
the operculum and dentition can decide the question. The new 
group may be thus diagnosed : 
Perostylus n. g. Gen. Char.: Shell cylindrical or pillar-shaped, 
thin, with decollated apex like that of a Rumina or Cylindrella; 
last whorl but little wider than the spire; aperture small, shaped 
like that of Fusus or Chrysodomus (Sip ho), produced in an open 
canal below ; columella straight or sinuous, without folds; outer lip 
thin and fragile. Type Cerithium ( Colina ) Brazieri Tryon. 
The decollation of the spire is not the result of erosion, as in the 
species of Potamides and Melaniidce, nor is the apex filled with a 
thick solid mass of shell-tissue as in those groups. In Perostylus 
the structure is like that of Rumina decollata or the West Indian 
Cylindrellas. 
The genus will consist for the present of two species. 
P. Brazieri Tryon. 
Shell cylindrical, white, fragile, hardly tapering, consisting of 61 
remaining whorls, each carinated and obtusely nodulous in 
the middle, and obsoletely spirally lirate. Last whorl with 
one or two spiral cords below the peripheral keel, and more 
distinctly spirally lirate, the base nearly smooth. Aperture 
one-third the length of the shell; outer lip thin and fragile, 
columellar lip distinctly sigmoid, smooth. Alt 21, diam. 
6 mm. 
Habitat, Port Darwin, N. Australia (John Brazier). 
If this shell could be reproduced in the form it would have were 
the earlier whorls not decollated, it would be by all odds the most 
attenuated Gastropod known, surpassing even the Terebras in the 
number of its slowly increasing whorls. The numerous young shells 
