MOLLUSCA OF INDIA. 03 



muscular impressions striate from side to side, arched sharply over 

 the central portion. 



The radula is very broad ; the central tooth (fig. 5) is very minute, 

 and so hidden by the larger laterals that I have only been able to 

 see it once. The lingual ribbon is extremely brittle, and generally 

 parts upon the central line. It becomes very difficult to see the 

 whole side at once and count the teeth ; and I have not been able 

 to count the exact number of rows, but they are considerably over 

 a hundred. The laterals (fig. 5 «) are all similar, minutely pectini- 

 form, on a curved edge, very closely set together, and exceedingly 

 numerous, very gradually decreasing in size to the outer edge ; 

 they are packed much closer than those shown in fig. 5 a. 



+ 170 . 1 . 170 + 



Their extreme minuteness is shown by four medians occupying 

 only 0*0005 inch ; five laterals the same space. 



This form of radula suggests a scouring habit of feeding ; its 

 breadth and evenness of surface working over a large area, and 

 into the irregularities of the surface of rocks and stones covered 

 with confervoid growth, would enable the animal to collect its food 

 more rapidly ; whereas in other genera the far larger central teeth 

 present a less yielding narrower surface, one better fitted to be a 

 leaf-rasping instrument. 



DiTEGELLA AssAMicA, Godwin-Austen. (Plate LXXVII. figs. 1-6.) 



Duryella assamica, G.-A., Journ. Linn. Soc, Zool. vol. xv. p. 29-1 

 (1881). 



Locality. Panipputer Tea-garden near Tezpur, Assam (two speci- 

 mens from Mr. Lumsden). 



Original descriitiion : — "Shell (fig. 1) very thin and membrana- 

 ceous, imperforate, depressedly conoid. Sculpture quite smooth, 

 with some slightly indistinct, oblique, shallow ribbing on the third 

 whorl. Colour olive-brown. Spire depressed. Suture impressed. 

 Whorls 4, rather rapidly increasing. Aperture ovate, oblique. 

 Peristome very thin, columellar margin not at all thickened. 



"Size: major diam. 9-5, minor diam. 8*2 ; alt. axis 4-4 mm." 



Animal. The overhanging lobe to the mucous pore is largely 

 developed. The pallial line (fig. 2) is distinctly marked by a double 

 row of oblong segmental divisions formed by three parallel appressed 

 lines or grooves, crossed at intervals by the main radiating grooves 

 leading to the dorsal side. The mantle-lobes, shown detached from 

 the body (fig. 3), are as in D. levicula, only that the left dorsal 

 lobe is divided into two distinct parts at about the middle of its 

 length, and the left shell-lobe shows that about the middle it is 

 expanded and much lengthened into a tongue-shaped process, for 

 in the drawing it is shown unevenly contracted by the spirit. 



Generative organs (fig. 6). The albumen-gland is pear-shaped 

 and well developed, with an expansion near the junction of the 

 hermaphrodite duct. The oviduct was greatly swollen and enlarged, 



PAKT VIII. H 



