232 



segments combined, rostral projection forming a small lamella transversely trun- 

 cated at the tip. Urosome nearly as long as the anterior division, genital seg- 

 ment attaining the length of the 3 succeeding segments combined, 2nd segment 

 forming behind, on the ventral face, a projecting fold; last segment smaller than 

 the preceding one, and having the anal opercle perfectly smooth. Caudal rami 

 about the length of the anal segment, and forming inside near the base a very 

 conspicuous rounded lamellar expansion, tip obliquely truncated, and firmly con- 

 nected with the bulbously dilated base of the apical seta. Anterior antennae 

 about the length of the cephalic segment, and composed of 9 well defined articu- 

 lations, 5 of which belong to the terminal part; 1st joint very large, occupying 

 rather more than 1 / 3 of the length of the whole antenna, 2nd joint produced 

 behind to a strong conical projection, terminal part about the length of the 3 

 preceding joints combined, its last joint much the largest. 1st pair of legs rather 

 slender, spine inside the 2nd basal joint far remote from the apex, outer ramus 

 much shorter than the 1st joint of the inner, and without any seta inside, last 

 joint smaller than the other 2, and armed with 2 spines and 2 geniculated setee; 

 distal joint of inner ramus scarcely attaining V* of the length of the proximal 

 one. The 2 anterior pairs of natatory legs of essentially the same structure, 

 outer ramus of moderate size and having no seta inside the middle joint and 

 only 2 spines outside the terminal one; inner ramus scarcely more than half the 

 length of the outer, with both joints narrow and subequal in length, the distal 

 one armed at the tip with a spine and 2 unequal setee, inner edge smooth. 4th 

 pair of legs with the outer ramus almost twice as long as that of the 2 preceding 

 pairs and very slender, each of the joints carrying inside a single seta; inner 

 ramus scarcely longer than the 1st joint of the outer, and having the proximal 

 joint very small. Last pair of legs exceeding in length l / s of the whole animal, 

 each plate produced at the postero-superior corner to a short tooth-like projection, 

 inside which 2 unequal hair-like setee are attached, outer edge straight and car- 

 rying 4 small setee, inner edge slightly arcuate and inflexed, with 2 small setee, 

 the one in front of the middle, the other near the end, the latter finely ciliated. 



Colour yellowish, with irregular brownish shadows. 



Length of adult female 0.80 mm. 



Remarks. As above mentioned, this form was at first described by Th. 

 Scott as a species of the genus Tetragoniceps of Brady, to which genus it cer- 

 tainly bears some affinity. Its separation from that genus may, however, be 

 regarded as fully justified, and this view is still more corroborated by the detection 

 of another species, to be described below, which agrees with the type in all 

 essential characters, though being evidently specifically distinct. 



