156 G. WESTERN ON ROTIFERS. 



variety of form whicli I tlien thought amounted to specific 

 difference is, I believe, due to the condition of the reproductive 

 system or to the repletion or otherwise of the digestive organs. 

 The Pterodina described by Dr. Barnett Burn in " Science 

 Gossip," 1889, p. 104, differs in some respects from that which I 

 consider the P. trmicata of Gosse (vide PI. XXV., Fig 4, Society's 

 Journal, January, 1892), and may possibly be another species, 

 but I have not as yet been able to find it. 1 have been much 

 assisted in this investigation by Messrs. Bryce and Percy 

 Thompson, both of whom appear to have been acquainted with 

 these forms of Pterodinge before my attention was directed to 

 them by Mr. Parsons. 



Philodina commensalis (sp. nov. mihi). 



Sp. Char. : Body smooth ; corona large with slightly bulging 

 neck ; eyes roud-ovate, oblique ; teeth two ; foot thick, abrupt ; 

 spurs large ; animal hyaline, colourless ; living on Asellus 

 vulgaris. Length -^^ in. 



In the January number of this Society's Journal, on PI. XXV, 

 Fig 2, Mr. Chapman has given a sketch of a Philodina, which I 

 also found living commensally on some Asellus. As there 

 appears to be no published description of this Rotifer it is 

 necessary to give it a name, and as I have never found it except 

 attached to Asellus, I propose to call it P. commensalis. At 

 first sight it much resembles a Rotifer macrurus, but it has 

 nevertheless more of the square compact form of a Philodina. 

 It is hyaline and colourless except for the contents of the 

 alimentary canal. The body is marked with the usual longi- 

 tudinal flutings, and merges abruptly into the longish thick 

 telescopic foot, which is armed on the penultimate joint with 

 conspicuous spurs, and terminates in the usual toes. The spurs 

 are peculiar in shape, having a distinct heel and being 

 separated by a gap, which is equal to about half the width 

 of the base of the spur. They are broadest at the base, then 

 contract slightly and again widen before tapering to the point. 

 The corona is large, measuring quite the width of the body 

 when the animal is swimming. The neck is thickened and 

 bulging. The frontal column is of the ordinary form. The 

 antenna tapers towards the extremity and is carried rather 

 backwards. Eyes are pale roud-ovate and set at an angle like 



