69 
PLEUROTOMARIA, Defrance. 
Gen. Char. A trochiform spiral shell, with an 
angular sinus near the middle of the outer lip, 
from which a band marked with lines of growth 
that indicate the sinus is carried round the 
whorls ; no beak or sinus at the base of the 
aperture ; a columella with or without an um- 
bilicus. 
A genus of shells only known in the fossil state ; the spe- 
cies vary much in the elevation of the spire, but are gene- 
rally short shells. It is named Pleurotomaria , because it 
bears the same relation to Trochus as Pleurotoma does to 
Fusus; some of the most elongated species occur in the 
Silurian system of rocks, others are met with in various 
parts of the series up to the greensand, where the newest is 
found ; they are most abundant in the mountain limestone, 
and not unfrequent in the lower oolite. The following is 
a list of the species already published under various names 
in the 1 Mineral Conchology ’ : Helix carinaius , tab. 1 0. f. 2 ; 
H. striatus , 1. 171. f. 1 ; H. cirriformis , t. 171. f. 2 ; Trochus 
angiicus , t. 142; T. punctate , t. 193. f. 1 ; T. elongatus , 
t. 193. f. 2-4; T. abbreviate, t. 193. f. 5; T.fasciatus , t. 220. 
f. 1 ; T. granulatus, t. 220. f. 2 ; T. sulcatus, t. 220. f. 3 ; T. 
ornate , t. 221. f. 1 ; T. bicarinate, t. 221. f. 2 ; T. reticula- 
te, t. 272. f. 2; T. Gibsii , t, 278. 
