38 . RHIOSTOMA. 



III. Rhiostoma Benson. 



Testa subdiscoidea , late umbilicata ; anfractus ultimus 

 solutus, lateraliter descendens; apertui-a libera, superne incisa 

 tubulo iraperfecto retroflexo riraam coronante. — Operculum 

 breviter cylindricum . multispiratum , apice plano , laevigato, 

 intus profunde excavatum. (B.) 



Rhiosloma*) Bens. in Ann. and Mag. n. h. .Sd. ser. V. p. 96: novum 

 genus Cyclostomaceorum. 



— Pfr. in Journ. Conch. X. p. 45. 



— W. T. Blanford in Ann. aud Mag. nat. liist. Jun. 1864. 

 Genus ut videtur naturale, e nonnullis speciebus Ptero- 



cyclo antea adscriptis bene constitutum, pluribus novis exinde 

 cognitis auctum. 



Species : 



214. 1. Rh. Hoiisei (Cyclo$«tOBtBa) HaisBe». 



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 convexi, cele- 

 riter accrescentes, ultimus antice longe solutus , descendens, 

 dorso carinatus; apertura obliqua, subcircularis; perist. sub- 

 duplex : internum superne incisura triangulari 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. (CoU. Nr. 44.) 



Cyclostoma f/ousei Haincs 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 Housci Bens. in Ann. and Mag. n. h. 3 d. ser. V. p. 97. 

 Habitat Siam (Dr. House), Camboja (Mouhot). 



215. 2. Ria. Haine^i Pfr. 



T. late umbilicata, depressa, solida, distincte et confierte 

 striata, (sub epidermide obscura) fuscula, flammulis angustis 



*) f/oKj^promontorium. 



