2 Transactions of the Society. 



forms a connecting link between the two genera (Ecistes and 

 Melicerta ; the upper half of its trochal disk being that of the 

 latter, while the lower half is that of the former. Seen from the 

 oral surface as in Fig. 2, no one would suppose it to be other than 

 a true Melicerta, living in a tube of faecal pellets ; but viewed from 

 the antoral surface as in Plate L, Fig. 1, its relationship to 

 (Ecistes is at once apparent, for though the upper half of the 

 trochal disk is deeply cleft into two lobes (just as in Melicerta), the 

 lower half is almost a single lobe, there being the slightest possible 

 hint of a notch at the lowest point. 



It would seem then, at first, as if this new species ought to 

 decide the point as to whether the five genera, (Ecistes, Limnias, 

 Tuhicolaria, Melicerta, and Cephalosiphon should be reduced to 

 one, as Gosse proposed nearly twenty years ago ; for as the 

 form of the trochal disk is one of the main differences between these 

 genera, the existence of a species possessing half the trochal disk 

 of one genus and half of another, shows, one would say, that the 

 separation of the genera cannot easily be maintained, Gosse 

 thought that the differences of the trochal disks, &c., were not 

 sufficient to warrant the formation of five genera of such similar 

 creatures, especially when, as was the case when he wrote, each 

 genus contained but one species. 



At the date of Gosse's paper, the five genera were repre- 

 sented only by (Ecistes crystalUnus, Limnias ceratophylU, Tuhi- 

 colaria naias, Melicerta ringens, Cephalosiphon Limnias ; but the 

 list now is extended as follows : (Ecistes crystalUnus, (E. longi- 

 cornis (H. Davis, 1857), (E. intermedius (H. Davis, 1867), 

 (E. pilula (J. G. Tatem, 1868), (E. umhella (F. Oxley, 1879), 

 (E. Janus (J. Hood, 1880) ; Limnias ceratophylli, L. annulatus 

 (Bailey) ; Melicerta ringens, M. tuhicolaria ( = Tuhicolaria naias 

 = M. Tyro) ; Cephalosiphon Limnias. 



The only genus with a single species now is the very weU- 

 marked one Cephalosiphon, and Mr. Hood tells me that he has 

 seen a new species of this genus on the weed from Loch Lundie. 



While admitting, then, the close connection of these genera, I 

 still think it would be inexpedient to reduce them all to one. 

 With the single exception of (E. Janus (and in its case only from 

 one point of view), the old genera are at once recognizable by their 

 trochal disks, and generally by their tubes. 



The new rotifer is, I think, an (Ecistes rather than a Melicerta. 

 It is true that Mr. Cubitt named Mr. Tatem's very similar rotifer 

 Melicerta pilula ; but that was because he was avowedly adopting 

 Mr. Gosse's suggestion of reducing the five genera to one : M. 

 pilula is a true Ecistes. 



No one who has watched (E. Janus open its trochal disk could 

 mistake it for a Melicerta. Like CE. umhella, and indeed like all 



