the Cyclostomacea of Eastern Asia. 445 
Mr. Benson suggested to us, some years since, that the cause 
of our being unable to detect the operculum in the perfectly 
fresh specimens obtained was, that it was retracted far within the 
aperture as in Diplommatina. Taking all the characters into 
consideration, there appears good reason to believe that this 
genus must be classed as an abnormal member of the Diplom- 
matina group. 
4. Crosrorutis, Bens. 
A single specimen of this genus, in which the last whorl 
descends freely, was obtained by Mr. Benson from Molmain. I 
have never had an opportunity of seeing the specimen, and 
know it by the description alone. Judging from that, and 
taking into consideration the abnormal character of the last 
whorl, which appears to present in its peculiarities the converse 
of Opisthostoma, there appears reason to believe that this 
minute form will also prove to belong to the Diplommatina 
group. 
Doubtless numerous species of these very minute genera have 
escaped the notice of collectors; for, unless most careful and 
special search is made for them, they will certainly remain un- 
observed, more especially if large and handsome forms occur in 
the same locality, and attract attention. 
Subfamily CycLorinz. 
I have long had reason to doubt the correctness of uniting 
the genera Cyclotus, Pterocyclos, and Alyceus into one sub- 
family. The Indian forms of the first genus always appeared to 
me to possess a considerable resemblance to Cyclostoma and 
Otopoma. Pterocyclos, on the other hand, is very closely allied 
to Cyclophorus; while Alyceus has no close affinity with any 
other genus, but appears to possess some slight points of agree- 
ment with certain Pupinine. The characters of the subfamily, 
moreover, as given by Dr. Pfeiffer, derived from the operculum 
alone, are only applicable to some of the genera included. These 
characters are :—‘‘Operculum crassum, e duabus laminis com- 
positum (exteriore plerumque calcarea, interiore cornea, ambabus 
sulco marginali separatis) orbiculare, arctispirum, nucleo cen- 
trali.” Now the operculum in all the species of Alyceus which 
I have examined (twenty at least) is thin, composed of a single 
lamina, and without any marginal sulcation. In Péerocyclos 
there is no duplication nor marginal sulcation ; and the opercu- 
lum in many species (e.g. P. Cumingi, Pfr., P. rupestris, Bis) 
cannot be said to be orbicular. For these several reasons I be- 
lieve that the genera united under this subfamily must be re- 
distributed. 
