672 Proceedings of the Royal Irish Academy. 



Family Teiaethru)^. 



Polyarthra platyptera, Ehrenb. This curious skipping Eotifer was^ 

 found abundantly in tbe lakes and bog-pools near Westport and 

 Castlebar during all •my visits. 



Anarthra, n. g. A. aptera, 'Koodi = Polyarthra aptera, Hood. Joum^ 

 Quekett Club, Oct. 1893, p. 281. 



(Plate XXII., figs. 1, la, lb.) 

 In this very anordalous Rotifer, the lateral spines or skip- 

 ping appendages are entirely absent. The systematic position 

 of the animal is accordingly a difficult matter to decide ; for 

 the possession of such spines is not only a generic character of 

 Polyarthra, but is a character common to all the hitherto 

 described members of the Triarthridse, while, on the other 

 hand, the whole conformation and organization of the creature 

 is in other respects identical with that of Polyarthra. Thus 

 it has a sac- shaped footless body ; the corona truncate, with a 

 single ciliary wreath ; a single large occipital eye ; the mastax 

 pear-shaped, and trophi forcipate. The corona is furnished, as 

 in Polyarthra, with two fleshy setose prominences, and in front 

 of each of these with a long style. Two small antennae are 

 situated low down in the middle of the back. From the very 

 close general resemblance to Polyarthra platyptera, I at first 

 placed this new species in the same genus : on reconsideration 

 it appears more convenient to isolate it in a separate genus, but 

 having regard to the general features of its organizatioUj to 

 leave it in close proximity to Polyarthra, as an aberrant mem- 

 ber of the family Triarthridse. I discovered this species in 

 1892 in a lake in Forfarshire, and on Aug. 1, 1894, I obtained 

 a few examples in a lake near Westport. These, as yet, are 

 the only records of the species. 



Triarthra longiseta, Ehrenb. I found numbers of this common and 

 graceful species in a lake at Castlebar in 1891, and in bog-pools 

 around Westport in 1892, '94. 



T. breviseta, Gosse. Many specimens of this tiny three-spined species 

 occurred in company with Brachionus ruhens in a quarry near 

 Westport, in July, 1894. 



Family Hydatinid^. 



Hydatina senta, Ehrenb. I met with a quantity of this large and hand- 

 some species in a duck -pond near Westport. The water was green 

 with Euglense, which this Rotifer seems habitually to feed upon. 



