CYCLOPHORIDS. 95 
This species differs from C. Taylorianus by its spire, which 
is rather turbinate, by the more deflected last whorl, by 
the umbilicus, which is much narrower, by the more distinctly 
duplicate peristome, and by the greater distance of the spiraculum 
from the peristome. Compare with Pterocyclos spiracellum. 
II. PTEROCYCLOS. 
Operculum subcartilaginous, many-whorled, spirally lamellated, 
concave inside. Shell broadly umbilicated, rather discoidal ; 
peristome generally double; the internal short, cut on the right 
margin, the external dilated above into a roof-shaped beak. 
Pterocyclos, Benson, in Journ. As. Soc. i. 1832, p. 11; and v. 
1836, p. 356; Zool. Journ. v. n. 20, 1834, p. 462; Ann. & Mag. 
2nd ser. i. p. 345; Gray, Syn. Br. Mus. 1840, p. 133, ed. 1842, 
pp. 71,91; Proc. Z. S. 1847, p. 182; Cat. Cycl. 1850, p. 11; Sow. 
jun. Conch. Man. ed. ii. p. 238 ; Pfeiffer, in Mart. & Chemn. ed. 
ii. tom. i. 19, p. 7, 193; Z f. I. 1847, p. 111, and 185], p.1; 
Troschel, in Z. f. M. 1847, p. 44; Z. f. 1. 1851, p. 1385; Consp. 
p- 7; Pneum. Mon. p. 41. 
Spiraculum, Pearson, in Journ. As. Soc. ii. 1833, p. 590. 
Steganotoma, T’vroschel, in Wiegm. Arch. f. Nat. 1837, i. p. 163; 
Philippi, Abild. i. 1844, p. 105. 
Myxostoma, T’rosch. bid. p. 44; Pfr. ibid. p.111; Gray, in Proc. 
Z. S. 1847, p. 182; Cat. Cycl. p. 14. 
Lituus, Martyn, U. C.1784; Hump. Mus. Calen. 1797; Gray, R. 
Z. Soc. 1847, 182. 
The species belonging to this genus may be arranged in the 
following manner :— 
A. Abnormal; 
1. With the peristome nearly simple .§1. N. 1. 
2. Peristome double; operculum exter- 
nally nearly flat, with the outer 
whorls raised in lamelle . : oh Be SaaS: 
SL. Genuine; operculum externally very con- 
vex, margin of the whorls forming spiral 
horizontal lamella . ‘ ; : »§ 3. ,, 416. 
§ 1. Peristome nearly simple. 
1. Prerocycios ? INCOMPTUS. 
Shell depressed, solid, coarsely striate, opaque, white, with a deci- 
duous brownish-horn-coloured periostraca ; spire little raised, 
with the apex prominent ; whorls 5, rapidly increasing, the last 
one cylindrical, obsoletely angulated ; umbilicus very broad ; 
aperture diagonal, nearly circular ; peristome simple, with the 
D 
