38 
RHIOSTOMA. 
214. 
215 . 
111. Rhiostoma Benson. 
Testa subdiscoidea , late umbilicata ; anfractus ultimus 
solutus, lateraliter descendens; apertura libera, superne incisa 
tubulo imperfecto retroflexo riraam coronante. — Operculum 
breviter cylindricum , multispiratum , apice piano, laevigato, 
intus profunde excavatum. (B.) 
Rhiostoma*) Bens, in Ann. and Mag. n. h. 3d. ser. V. p. 96; novum 
genus Cyclostomaceorum. 
— Pfr. in Journ. Conch. X. p. 45. 
— W. T. Blanford in Ann. and Mag. nat. hist. Jun. 1864. 
Genus ut videtur naturale, e nonnullis speciebus Ptero- 
cyclo antea adscriptis bene constitutum, pluribus novis exinde 
cognitis auctum. 
Species: 
1. Rli. Hovisei (Cyelostoiiia) Haiaies. 
T. late umbilicata, subconoideo-depressa , solida, leviter 
striatula, sub epidermide tenui, cornea, decidua alba, strigis 
crebris angustis, angulatis, fuscis picta; spira parum elevata, 
obtusula; sutura profunda, canaliculata ; anfr. 5 convex!, cele- 
riter accrescentes, ultimus antice longe solutus , descendens, 
dorso carinatus; apertura obliqua, subcircularis; perist. sub- 
duplex : internum superne incisura triangular! et foramine 
extus in tubulum subrectum retroflexum abeunte notatum. 
externum supra incisuram continuum, undique vix expansum, 
— Operc. cyathiforme , intus profunde excavatum , extus 
acute 6 — 7-spiratum, nucleo (in vetustissimis) lato convexo laevi- 
gato. — Diam. maj. 26 — 33, min. 21 — 24, alt. 12 — 13 mill. 
Apert, diam. 9 — 10 mill. (Coll. Nr. 44.) 
Cyclostoma Housei Haines in Ann. Lyc. N. York VI. p. 157. t. 5. 
f. 12—15. 
Pterocyclos Housei Pfr. Mon. Pneum. Suppl. p. 29. 
— — Reeve Conch, ic. sp. 21. t. 4. 
Rhiostoma Housei Bens, in Ann. and Mag. n. h. 3d. ser. V. p. 97. 
Habitat Siam (Dr. House), Camboja (Mouhot). 
2. Rh. Hainesi Pfr. 
T. late umbilicata, depressa, solida, distincte et conferte 
striata, (sub epidermide obscura) fuscula, flammulis angustis 
*) ^/oyj' promontorium. 
