io8 
Memoirs of the Indian Museum. 
[VOL. II 
Mouth parts. — Outer maxillœ very broad, almost quadrangular, with a fringe of 
hairs at the extremity. Palp broadly conical, with a few fine hairs on the dorsal edge 
and a bunch of stouter ones at the tip. Maxilla with a shallow and narrow incisure 
on its free edge, bearing externally to the incisure three stout spines, of which the 
outermost is the stoutest; at the base and on the inner edge of the incisure several 
bristles, and internally to it about ten to twelve spines of different lengths, the first 
or second and the last being the stoutest ; the ventral edge fringed with fine hairs. 
Mandibles normall}^ with five teeth, the two innermost of which (inner angle) are 
close together, while the outermost, which is much .stouter than the others, is widely 
separated from them ; the two innermost teeth covered with fine, short hairs. 
Labrum feebly bullate, apparently without chitinous teeth. 
The anatom^^ of this species closely resembles that of Pcecilasma minutum in 
several respects, but differs in others, notably as regards the maxillæ. The 
Carina resembles that of P. excavatum and P. dubium. My description is not so 
different from Lanchester’s as it might seem to be on casual inspection, but, having 
examined a large number of specimens from different hosts and different localities, 
I have been able to note a considerable amount of variation, especially as regards 
the development of the valves. Lanchester, in dealing with the mouth parts, has 
obviously called that end of the free edge I have called inner, outer, and vice versa. 
The whole of the free edge internal to the incisure is on a higher level than the base 
of the incisure, which is very shallow, but also than the base of the three stout spines 
external to it. These spines are a feature common to a good many species both of 
Pcecilasma and of Dichelaspis , the two inner ones being parallel to one another — not 
arranged in a linear series. 
At first, when dealing with the specimens of this species, I thought that they 
represented two distinct species or varieties; but, with the whole series before me, 
including a number from Sumatra which Dr. van Kämpen has been kind enough to 
send me, I find it impossible to discover a definite break at any point. The two 
individuals figured represent the extreme forms that the species assumes, while the 
one figured by Lanchester was intermediate in .some points. The exact outline of 
the capitulum is a variable character, and so is the appearance of the valves, which 
are translucent in .some specimens and opaque in others. A common feature is a 
white vertical bar, often very indistinct, on the capitulum near the upper part of the 
occludent margin. 
Aurivillius’s Pcecilasma tridens was evidently a young example of the species. 
The length of the peduncle is a variable character, although I have only seen it 
quite so long in one specimen as it appears to have been in the type of P. tridens. 
Aurivillius says that the mandible has no incisure, but in my specimens the incisure 
is often so shallow that it may very easily be overlooked. I hesitated, however, 
to sink Lanchester’s name as a synonym without seeing specimens from the 
Philippines, until I found a young specimen from the Orissa coast agreeing in every 
respect with Aurivillius’s figures and accompanied by others resembling those of 
Lanchester. 
