143 



Triarthra Brachiata, a New Species of Rotifer, and Remarks 

 ON the Spines of the Triarthradae. 



By Charles F. Rousselet, F.R.M.S. 

 {Read Octohev IHth, 1901.) 



Plate 8 (Lower Portion). 



The genus Triarthy^a contains three w^ell- marked species, which 

 are distinguished chiefly by the length of their skipping spines 

 relative to the body. Triarthra longiseta has a small body 

 (130 — 175 iL = ^0^ — xio ^^- i^^ &vLe) and very long spines, 

 twice to four times the length of the body. A very long-spined 

 variety, which often occurs in very large lakes, has been called 

 var. limnetica by Dr. Zacharias, but it seems to me the variation 

 is too slight even for a variety. Triarthra mystacina has a larger 

 and stouter body (204 /x = -^-^ in. in size), with spines 1-i- to If 

 times the length of the body ; whilst the third species, Triarthra 

 hrevispina^ is very small (size 102 /x = ^i^- in.) and has very 

 small, narrow spines, only about one- quarter the length of the 

 body in size. 



Two other species which have been named are undoubtedly 

 synonyms : T. cornuta Weisse being the same as bi'evisjnna, and 

 T. terminalis Plate seems to be longiseta. 



For some years past I have occasionally come across a small 

 Triarthra which is different from any of the above species. It 

 is slightly smaller in length and less broad than brevispina, thus 

 appearing more elongated in shape, and has longer spines, fths to 

 fths the length of the body, and which are moreover very broad 

 and arm-like at the base, as will be seen from fig. 7, PI. 8. 

 From this peculiarity T have named this new species T. brachiata. 

 The broad bases of the spines appear to encompass the body at 



