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 fresh specimens obtained was, that it was retracted far within the 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. Clostophis, 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 CycLOTiNiE. 



I have long had reason to doubt the correctness of uniting 

 the genera Cyclotus, Pterocyclos, and Alycaus 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 Alycaus has no close affinity with any 

 other genus, but appears to possess some slight points of agree- 

 ment with certain Pupininse. The characters of the subfamil}^, 

 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 Alycaus which 

 I have examined (twenty at least) is thin, composed of a single 

 lamina, and without any marginal sulcation. In Pterocyclos 

 there is no duplication nor marginal sulcation ; and the opercu- 

 lum in many species (e. g. P, Cumingi, Pfr., P. rupestris, B.,) 

 cannot be said to be orbicular. For these several reasons I be- 

 lieve that the genera united under this subfamily must be re- 

 distributed. 



