1866.] MR. W. T. BLANFORD ON OPISTHOSTOMA. 449 



verticalis, subtrigonali-rotundata ; peristoma simplex, undique 

 expansum. Operculum normale. 



Diam. incl. peristom. 1*5 mm. ; perist. non incl. ] mm.; alt. 

 1'5 mm. ; aperturse diam. circa - 5 mm. 



Hab. prope Khandalla ad summos montes "Syhadri" si ve West- 

 ern Ghats appellatos, inter Bombay et Poona, Indise orientalis. 



The animal was very difficult to observe, on account of its extreme 

 shyness and minute size. Only a very small portion of the body 

 was extruded from the shell. The foot is very short and apparently 

 rounded, but could not be seen fairly, as the animal would not crawl 

 up a glass but appeared to endeavour to hide itself amongst decayed 

 leaves. The tentacles are short and blunt, the eyes at their outside 

 base, rather high in position, but not nearly so much so as in the 

 Aciculacece. The whole animal is white and translucent, the eyes 

 appearing as black specks, perfectly sessile. After two or three 

 failures I succeeded in examining an operculum by breaking back 

 the whorls of a specimen carefully until I came to it. It is lodged 

 at the constriction in the last whorl, as long since suggested by Mr. 

 Benson, and is distinctly horny, concentric, and paucispiral, resem- 

 bling the figure of the operculum of Diplommatina folliculus given 

 in Adams's ' Gen. Rec. Moll.' This entirely confirms the views I 

 long since expressed as to the close affinity of Opisthostoma to Di- 

 plommatina, and shows the former, moreover, to be nearer to the 

 typical costulate Diplommatina; of the Himalaya than to the smooth 

 or spirally lirate species (Arinia, H. & A. Ad.) of Hindustan, as the 

 latter have the spiral structure apparently obsolete*. It is worthy 

 of remark that some of the Pupinidae (e. g., Pupina artata, Bens.j, 

 when their opercula are examined by transmitted light, show an 

 apparently paucispiral structure, due to the whorls increasing in size 

 more rapidly near the centre ; but the construction of the spiral in 

 Pupina and Cataulus has been shown to be different from that 

 which obtains in other forms of operculated land shells. 



The characters which serve to distinguish Opisthostoma fairbanki 

 from O. nilgiricum are : — 



1 . The greater exsertion and smaller excentric deflection of the two 

 apical whorls of O. fairbanki. 



2. The simple expanded peristome and subtrigonally rounded 

 aperture — O. nilgiricum having a non-expanding duplicate peristome, 

 the outer portion retro-relict, and a circular aperture. 



3. The more distant sculpture. 



4. The manner of curvature of the last whorl, the posterior bend 

 of which is much more acute in the present species. In O. nilgiri- 

 cum the posterior half of the sigmoid curve of the last whorl is more 

 open than the semicircular curve nearer the aperture, the umbilicus 

 being fully exposed within the former. In O. fairbanki the anterior 

 curve is the more open, and the last whorl just in front of the pos- 



* I have just cut out the opercula of two specimens of Diplommatina pachy- 

 cheilus, Bens., from Darjiling, and find the spiral structure much less distinct 

 than it usually is in the Cyclophoridae. 



