39 24 Proceedings of the Royal Irish Academy. 



side, where there is a fine forwardly directed hair close to the base of the 

 segment. The fifth segment is blunt at the apex. 



As may be clearly seen in the figure (PL II., fig. 12a), the legs of this 

 species are much shorter and stouter than in F. musculns; segments 2-5 of 

 the last three pairs are more or less clavate at the extremities. 



The swimming-hairs are remarkably well-developed. There are three long 

 terminal spines at the end of the fourth pair of legs ; the longest of these 

 usually equals or is slightly longer than the sixth segment, whereas in 

 F. musculus it is shorter. One of these terminal spines is much shorter than 

 the other two, and all of them appear, under a high magnification, to be finely 

 pectinated. 



Male. Specimens which are presumably the males of this species appear 

 to differ from the females only in their smaller size, as far as the external 

 characters are concerned. 



Nymph. — A Frontipoda nymph dredged from shallow water in Castlebar 

 Lough is, judging by its short, robust legs and other characters, to be referred 

 to the present species. 



This example measures - 495 mm. in length by '253 mm. in breadth. 



The legs, palps, and highly chitinized parts of the body were of a greenish 

 tint in the living mite, the coecal area being yellowish, surrounded by a 

 darker brown colour. The large black-pigmented eyes are situated on the 

 front margin of the body, and when viewed from above they show clearly 

 through the dorsal plate. 



The general form (PL II., fig. 12A) is oblong, narrowed, and evenly rounded 

 in front, and somewhat truncated at the end of the bod}'. The dorsal surface 

 has a thickly chitinized rim, and is slightly sinuate at the posterior margin. 

 There is a comparatively wide dorsal furrow with sinuate margins between 

 which and the side margins of the body there are at least four pairs of 

 large hair-bearing glands, while in the groove itself are embedded five more 

 pairs of these glands. Two long bristles are present on both the upper and 

 lower front margins of the body. The ventral area is very similar to that of the 

 nymph of Frontipoda musculus figured by Koenike (10, PL XIV., fig. 9), except 

 that the end of the body is produced in a truncated manner, and is longer. 

 The apex of the first epimeron is capped by two broad, spade-shaped spines, 

 one lying immediately behind the other, and the edges of these are extremely 

 finely serrated, much as they are in Oxus ovalis (0. F. Muller). 



The provisional genital area carries the usual four discs, the inner margins 

 of which are flattened. There are four hair-bearing glands surrounding the 

 anal plate (PL II., fig. 12c). 



Localities. — Lake at Barley Hill near Westport amongst Myriophylluni and 



