1921.] B. Prashad : Sitmatraii Molluscs. 473 



points are beautifully illustrated by the large Sumatran collection 

 before me and I include below a few notes regarding the shells of 

 different types from the various localities. 



Most of the shells are from fresh-water areas on the outskirts 

 of Deli. They consist of many lots collected at different times 

 by Mr. den Doop and Mr. J. B. Corporaal at Medan, Medan Estate, 

 Padang Boelan and Mariendal Soengei. These lots mclude shells 

 of different types, varying in colour from pale yellow to dark 

 brown and even black. The last are of this colour owing to a 

 black deposit on their surface. The sculpture also is variable, some 

 of the shells are quite smooth, others have delicate oblique striae 

 more marked on the body- whorl than elsewhere, while in some 

 cases the striae are so prominent as to look like low ridges. The 

 shape of the aperture is also different, in some shells it is nearly 

 subcircular, not much higher than broad, in others it has a 

 distinct campanulate appearance, while others still show a distinct 

 angulation, making the curvature much less regular but more 

 prominent and the upper side rather straight. Young Physa-\\ke 

 shells in the earlier stages of development as recorded by Annan- 

 dale' and Germain among Indian specimens are also present. A 

 few shells resemble the coroinandclicus form, others are identical 

 with zebrimts, and a few others resemble the &gures oi brunneus 

 and cburiiciis in Sowerby's monograph. 



Other Sumatran localities from which the species was collected 

 are rice-fields at Perbaoengan (Serdang) ; Serdang Estate ; Batang 

 Kwis ; in a fresh-water lake near Perbaoengan ; Anak Laut (in 

 the isle of Sabang) ; and a streamlet near Timbang Lankat. 

 These shells are also of the same types as the ones from Deh, 

 except those collected from the Timbang Langkat streamlet, which 

 are rather smaller, have a smaller mouth and have the striae on 

 the surface much coarser. 



The following are the measurements (in millimetres) of some 



shells from various localities : — 



», .^ Height 



Locality. Maximum Minimum Total Diameter of aper- 



diaiiieter. diameter. Height, of aperture. ture. 



1. Medan Estate 12 10 5 5"8 6 



2. Near Medan ... 15-7 13 6'8 6-9 7-8 

 ,^. Rice-fields (Ser- 

 dang) ... 1^-6 12-2 6-.S 6"4 77 



4. Padang Boelan ... ij-c: i^-^ 6 6'8 8*6 



5. Near Perbaoengan. ii-i; ^-5 5-5 6 6'8 



6. Streamlet at Tim- 



bang Langkat ... iq-i 8'4 5'f> 4"f' 6*5 



Genus Gyraulus, Agassiz. 

 Gyraulus convexiusculus (Hutton). 



1897. Planorbis compressus, v. Martens, o/>. ciL, pp. 13, 14, pi. i, figs. 

 17-21 ; pi. xii. figs. 7. 10. 



1 Rec. Ind. Mus. XIV, pp. in, 112, figs, i, la {1918). 



