16 
CYCLOTUS. 
I. Operculum testaceum. Genera: Lithidion , Otopoma , 
Cyclostomus , Tudor a , Leonia. 
II. Operculum cartilagineum , extus strato tenui testaceo 
tectum. Genus : Cistula. 
III. Operculum pure cartilagineum. Genus : Chon - 
dropoma. 
IV. Operculum duplex, intus concameratum. Genus: 
Pomaiias. 
V. Operculum corneum. Genera: Realm , Omphalotro - 
pis , Bourciera. 
A. Operculum circulare, saepe extus concavum, anfrac- 
tibus multis lente accrescentibus formatum, nucleo centrali. 
I. Cyclotus Guilding. 
Operculum orbiculare, testaceum, arctispirum, extus con- 
caviusculum, margine anfractuum subincrassato vel in laminam 
incurvatam elevato, nucleo subcentrali. — Testa subturbinato- 
depressa vel discoidea; peristoma continuum vel marginibus 
callo junctis, simplex vel duplicatum, rectum vel expansum. 
Cyclotus Guild, in Swains. Malac. p. 186. 336.*) 
— Gray Syn. Brit. Mus. Ed. 1842. p. 91 ; Proc. Zool. Soc. 1847. 
p. 182 et Catal. Cycloph. p. 5 
— Herrmannsen Ind. gen. Malacoz. I. p. 350. 
— Pfr. in Z. f. M. 1851. p. 132; Consp. p. 4. 
Aperostoma Trosch. in Zeitschr. f. Malak. 1847. p. 44. (ex parte.) 
— Pfr. ibid. 1847. p. 47. 104. 
Cyclostoma spec. Auctt. 
Species hue pertinentes sequente modo distribui possunt: 
I. Peristomate simplice, 
a. recto §. 1. Nr. 1 — 25. 
b. expanso §.2. — 26 — 34. 
II. Peristomate duplicato . . . §.3. — 35 — 45. 
§. 1 . 
1. C. giganteus Cray* 
T. late umbilicata, subdepressa, solida, confertim rugoso- 
striata, sub epidermide corneo-fulva, fasciatim decidua alba; 
*) Nearly discoidal; pillar none; spire scarcely raised, and the tip ob- 
tuse ; a small siphon at the top part of the aperture. Types : C planorbulus 
Enc. m. 461. f. 3. — C. vanegatus Srv. , Sow. Gen. f. 1 . (Swains. 1. c.) 
