2 I . F. ROUSSELET ON TETRAMASTIX OPOLIENSIS (ZACHARIAS). 



laterally, as figured by Zacharias), the dorsal spine being much 

 longer than the ventral spine. 



The integument is somewhat stiffer than in the other members 

 of this family, and presents a transition towards the loricate 

 rotifers. 



In a previous paper* I have stated my views of the use of 

 the long spines of the Triarthradae, which are of no use for 

 progression, but are certainly protective in character, and pre- 

 vent their possessors being too readily swallowed by such foes as- 

 Asplanchna. The long spines also give the animal a greater 

 floating power, so that it does not sink in the water so readily, 

 and enable the creature to maintain itself in the open water 

 with less ciliary effort than would be necessary in the case of 

 a similar rotifer without these appendages. 



The general anatomy of Tetramastix opoliensis is normal, as 

 can easily be seen from the figure, and requires no remarks on 

 my part. I am glad to be able to describe and figure these 

 additional features, which correct and complete our knowledge of 

 this interesting species. 



Tetramastix has, therefore, so far been found three times: in 

 the Oder, near Oppeln (1897) ; in a pond near Tabor, in Bohemia 

 (1899) ; and in a pool in the Matopos, Rhodesia (1905). 



The measurements of the largest Rhodesian specimen were as 

 follows: body alone, 204 fx ( T ^- in.); large anterior spine, 374 /x 

 (~ in.) ; large posterior spine, 272 \x (— in.). Mr. Hlava's 

 specimens seem to have been a little smaller in size, but stouter 

 in body : body alone, 169 p. ( T i^ in.) ; large anterior spine, 254 /x. 

 {jjy-Q in.) ; large posterior spine, 169 /x ( T i^- in.). 



I reproduce also the figure of the contracted specimen, drawn 

 by Mr. F. R. Dixon-Nuttall. 



Explanation of Plate 34. 



Fig. 1. Tetramastix opoliensis (Zacharias), latero-ventral view 

 when swimming, x 280 ; drawn from life by S. Hlava.. 



,, 2. Do., fully contracted, x 185; a preserved specimen from 

 Rhodesia, drawn by F. R. Dixon-Nuttall. 



,, 3. Do., the jaws; drawn by S. Hlava. 



1 " Triarthra orachiata, a New Species of Rotifer, and Remarks on the 

 Spines of Triarthradae." Journal of the Quthett Microscopical Club, Vol. 8, 

 November, L901, pp. 143—145. 



Jour . U Microscopical Club, Sir. 2, Vol. IX., No. 59, November 1906. 



