1872.] 
2G5 
F. Stoliczka — On the Cyclostomacea of Penang. 
Genus. OPISTIIOPOKUS, Bens. 
There is no apparent distinction between the shells of Opisthoporus and 
those of Spiraculum. A cursory examination of the animals of a few species 
also shewed, that no essential distinction exists in the general anatomical 
structure, and hut a very slight one in the dentition. 
The only difference, which as far as known is a constant one, consists 
in the structure of the operculum. In the former genus this is discoid, 
horny on the inner side, calcareous on the outer, and composed of spiral 
lamin® entirely covering a tube. In Spiraculum the upper spiral layer is 
also generally calcareous, and more or less elevated, but the spiral canal 
is always open, not forming a closed tube. The former structure of the 
operculum is peculiar to Gyclotus, the latter to Pterocyclus and some species 
of Oyclophorus. 
OrisTiioPonrs Pestaitgensis, n. sp. PI. X, Fig. 7. 
O. testa sub-discoidea, apice paulum exserta, latiuscule umbilicata, corneo 
solidula ; anfractibus 4'5 ad 5, teretibus, sutur a profunda junclis, epidermide 
brunnea vel nigrescente, transversvm confertissime striata, in ultimo an- 
fractu ad peripheriam superam et inf cram breviter ciliata, indutis, sub epi- 
dermidem albescentibus atque strigis transfer sis, brunneis vel fuscis, paulo 
undulatis, aut plus minusve acute angulatis, notatis ; apice sub-mammillato, 
nigrescente vel 'pall lido ; umbilico modico,fere dimidium Jatitudinis anfractus 
penultimi exponente ; ultimo anfractu ad aperturam valde descendente, sed 
baud dissoluto, ad suturam tubalodjrcvi tenuique, secpissime retrorsum curvato, 
rare fere verticali, rarissimeque antice versus directo, in specimmibus adultis 
circa 15 ad 2 mm. a margins aperturali distante, instructo ; apertura cir- 
culari, ampla, obligua, peristomate in junioribus simplici,in adultis breviter 
bilabiato, margins lahii interni paululum incrassato, gape rubcscente tincto, 
baud distincter discreto, externo expansiusculo ; ambobus supra paulum pro- 
ducts atque prope suturam modice inslnmtis. Operculum discoideum, 
interne fix, externe dislinctc, concavum et album, multispiratum, medio 
corneo-testaceum, laminis duabus separate ad peripheriam acutissimis. 
Diam. maj. 11'5 ; diam. min. 9'5 S altit. testa G’G ; diam. apert. int. 4, 
extern <e cum perist. 4'7 m.m. 
This species is evidently closely allied to E. v. Martens’ O. Sumatra- 
nus* which is of nearly exactly the same size, hut its whorls are decidedly 
thinner and on the upper side more flattened, the upper apertural margins are 
considerably more produced, the plaiu of the aperture being, therefore, more 
oblique to the axis, while the sutural tube appears to he more distant from 
the margin. The direction of the tube was observed in four specimens of 
O. Sumatranus to he nearly vertical, while in about eighty specimens of the 
* Preuss. Expect naeh Ost-Asien., Zool. Theil, vol. II, p. 112. 
