the Cyclostomacea of Eastern Asia. 451 
other instance of the affinity of the hill-fauna of Southern India 
to Malayan types. 
9. SprRAcULUM, Pearson; and 10. OristHoporus, Bens. 
The genus Spiraculum, distinguished by the possession of a 
retroverted sutural tube open at both ends, and by a modification 
of the form of the mantle corresponding to the same, has, I 
think, better claims to generic distinction from Péerocyclos than 
_ even Rhiostoma. Its claim to separation from Pterocyclos I 
believe equal to that of Opisthoporus from Cyclotus ; and I should 
be inclined to class Opisthoporus as a subgenus of Spiraculum, as 
I have little doubt that the animal of the former genus, when 
examined, will be found to be similar in structure to that of the 
latter. 
Mr. Benson has lately described, under the name of Opistho- 
porus Gordoni, a species from Molmain, in Burma, which may, 
I think, very possibly prove to be a Spiraculum, when the oper- 
culum is obtained, as the known geographical range of forms 
belonging to that genus approaches far nearer to Molmain than 
that of Opisthoporus. To whatever type it may belong, it serves 
admirably to illustrate the extremely close affinity between them, 
since there is no character possessed by it which may not be 
found in one or the other form of each genus. S. dvanum, W. 
Blanf., has a duplicate lip and a smooth surface ; while an un- 
described species occurring in Assam has the last whorl free for 
a longer distance than in any known species of Opisthoporus ; 
and it has also a more prominent projection from the upper 
portion of the peristome. The sole difference between the two 
genera is in the structure of the operculum. 
11. Rutostoma, Bens. 
The projection from the upper portion of the peristome in this 
species differs from that in Spiraculum and Opisthoporus in being 
accompanied by a deep incision in the inner peristome, clearly 
showing that it is the homologue of both wing and incision in 
Pter ocyclos, and of both projection and sutural tube in the first- 
mentioned genera. In R. Housei, Pfr., the projection indeed 
forms a perfect tube. Rhiostoma is doubtless a good type, 
although species may very probably be met with connecting it 
with Pterocyclos more closely than is now the case. A single 
species (R. Haughtoni, Bens.) is found at Molmain; all others 
are Malayan. 
12. Autoroma, Troschel. 
I have no especial remark to offer upon this genus, which has 
not hitherto been met with out of Ceylon. 
