1919. ] N. ANNANDALE & B. PRASsHAD: Mollusca. 61 
extensive than Simpson (oP. cit., p.855) stated, extending from the 
mountains of Afghanistan to Ceylon and from Seistan to Burma, 
possibly even to Java and South China. 
Dead shells were found in very large numbers at the following 
places in Seistan :—at the edge of the Hamun near Lab-i-Baring, 
in pools in the desert near Nasratabad, in the bed of Randa 
stream near Jellalabad about twelve miles to the north and in a 
large backwater of an effluent of the Helmand some miles to the 
south-east of the capital. They were also observed on the surface 
and buried in the stiff clay of open plains near Jellalabad which 
are periodically flooded. Specimens from still water, including the 
Hamun, belong to phase B. those from water directly connected 
with larger streams to phase A. 
All these shells were in a remarkably good state of preserva- 
tion, and their surface was not at all eroded. In many instances 
the valves adhered tightly together and the molluscs had every 
appearance of being alive. Indeed, many of them were brought 
us as containing the animal by herdsmen at Lab-i-Baring, and 
the people were evidently surprised when we opened them and 
found only mud inside. It is probable that the animal burrows 
deep into the mud at the approach of winter and in this connec- 
tion the gape in the lower margin of the shell of many old indivi- 
duals is of considerable interest, indicating that the foot is particu- 
larly large and powerful. 
The shells give an indication of the age which the form habi- 
tually reaches, but this indication is open to two interpretations. 
On all the larger shells examined three very distinct regions can be 
distinguished. Round the umbo there is a region about 25 mm. 
wide by 13 mm. high in alarge shell. The sculpture of this region, 
though clear-cut, is almost microscopic. It includes the nodulose 
and sloping ridges characteristic of the species, and also numerous 
(about 16) concentric longitudinal striae, each of which is com- 
pound. This region has a smooth appearance as a whole and is 
always of a pale colour. The next region is a broad band about 
60 mm. broad by 24 mm. high in a large shell. Its general appear- 
ance is similar to the first region, but the epidermis becomes darker 
towards the lower margin, and it bears about the same number of 
compound striae. The third or outer region is about 30 mm. deep 
and occupies the full width of the shell. It has a much rougher 
appearance than the other two and bears four to six bands or 
groups of compound striae separated by smooth grooves. We are 
able to state definitely that the first region represents the growth 
of more than a year From the situations in which fresh shells are 
found in winter, where we may confidently believe they occur living 
in the flood-season, it is clear that the animal commonly undergoes 
a fairly prolonged period of hibernation, and in all probability it 
breeds when the floods are at their height in April or May. We 
found several shells in November that correspond precisely with 
the first region in the adult shells, and one of them still contained 
remains of the soft parts. Allowing for the period of free larval 
