16 CYCLOTUS. 
I. Operculum testaceum. Genera: Lifhidion , Otopoma, 
Cyclostomus, Tudora, Leonia. 
II. Operculum cartilagineum, extus strato tenui testaceo 
tectum. Genus: Cistula. 
III. Operculum pure cartilagineum. | Genus:  Chon- 
dropoma. 
IV. Operceulum duplex, intus concameratum. Genus: 
Pomatias. 
V. Operculum corneum. Genera: Aealia, Omphalotro- 
pis, Bourciera. 
A. Operculum circulare, saepe extus concavum, anfrac- 
tibus multis lente accrescentibus formatum, nucleo centrali. 
|l. Cycotus 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. 
"A perostoma Trosch. in. Zeitschr. f. Malak. 1847. p. 44. (ex parte.) 
-— Pfr. ibid. 1847. p. 47. 104. 
Cyclostoma spec. Juctt. 
Species huc pertinentes sequente modo distribui possunt: 
I. Peristomate simplice, 
a. recto $ 1.Nr. 1—25. 
b. expanso dbolegieuiruo LCS MO OE 
II, Peristomate duplicato . . . $.3. — 35—45. 
S E 
1. €. giganteus Gray. 
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 ofthe aperture. Types: C. planorbulus 
Ene. m. 461. f. 3. — C. variegatus Sm. , Sow. Gen. f. 1. (Swains. 1. c.) 
