io8 Memoirs of the Indian Museum. [Vol. II 



Mouth vkrts. — Outer maxillce 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 normally 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. 

 Lahrum feebly buUate, apparently without chitinous teeth. 



The anatomy of this species closely resembles that of Pœcilasma miniitiim in 

 several respects, but differs in others, notably as regards the maxillae. The 

 carina resembles that of P. excavatîim and P. dubium. My description is not so 

 different from Ivanchester'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 

 Pœcilasma 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 Kampen 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 Lranchester 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 Pœcilasma 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 

 lyanchester. 



