the Cyclostomacea oj Eastern Asia. 443 



position of Diplommatina, of all the Ci/cloiina, and of the Indian 

 forms ascribed to Hydrocena, 



1. Truncatella, Risso. 



Only a single species of this genus {T. Ceylanica, Pfr.) is 

 known to inhabit Ceylon, and none have as yet been met with 

 elsewhere in India. The species, so far as I am aware, presents 

 no peculiarities. 



2. Diplommatina, Bens. 



Dr. Pfeiffer, in his monograph, placed this genus between 

 Alyccms and Megalomastoma ; in the Supplement, he makes it 

 the type of a totally distinct family, of the suborder Opisthoph- 

 thalma, which is characterized by the eyes being placed above 

 the base of the tentacles. I have never seen living specimens of 

 any of the Aciculida; but, judging from the plates in Adams's 

 * Gen. Rec. Moll.,' the position of the eyes is very similar to that 

 seen in the Auriculacea. This is by no means the case in Di- 

 plommatina, in which genus the eyes, although higher in position 

 than in other Cyclostoraaceous genera, are rather at the side of 

 the head than above it ; and there is no trace of the long pro- 

 boscis of Truncatdla. The operculum also is concentric and 

 horny ; but, from the minute size of the species, and the manner 

 in which the operculum is withdrawn far within the shell, it is, 

 in most cases, difficult to examine it. In some species, as in 

 D. Nilgirica, W. & H. Blanf., the spiral structure is obsolete. 



The Indian Diplommatina may be divided into two groups, 

 with distinct geographical distribution. The more numerous 

 type inhabits the Eastern Himalayas and Burma, and comprises 

 the following species : — 



D. pachycheiltis, Bens. Sikkim. 



D.pullula, Bens. Sikkim. 



Z>. Blanfordiana, Bens. Sikkim. 



D. diplocheilus, Bens. Khasi Hills. 



D. polypleuris, Bens. Khasi Hills. 



D. exilis, W. Blanf. Ava. 



D. Pappensis, W. Blanf, Ava. 



D. sperata, W. Blanf. Pegu ; 



and two other species from Pegu as yet undescribed. These are 

 all characterized by a continuous peristome (the upper portion 

 being broadly appressed on the penultimate whorl), the presence 

 of a columellar tooth, and by strong transverse (vertical) costu- 

 lation on the whorls. The antepenultimate whorl is far broader 

 than the rest, and the spire above it is more or less acuminate. 



The two species from the peninsula of India described by my 

 brother and myself, viz. D. Nilgirica from the Nilgiri Hills, and 



29* 



