371 



ON MOTHOLCA TRIARTHROIDES SKORIKOW, CATHYPHA 

 BRACHYOACTYLA STENROOS, AND ON A NEW 

 BRACHIONUS FROM DEVIL'S LAKE, NORTH 

 DAKOTA. 



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



iliead March 'lUh, 1912.) 



Plate 13. 



Nothoica triarthroides Skorikow (Plate 13, figs. 1, 1). 



In 1 905 A. S. Skorikow gave a description * of a strange species^ 

 of Nothoica, which he had found in the River Neva near St, 

 Petersburg, in April 1903, and to which he gave the name 

 Nothoica ti'iarthi'oides. About the same time Dr. Skorikow sent 

 me a few specimens for mounting, and before returning the 

 mounted slide I forwarded it to Mr. Dixon-Nuttall, who made 

 the accompanying sketch (Plate 13, Fig. 1) of this peculiar 

 Rotifer. As a figure of it has not, as far as I know, been 

 published, E take this opportunity of supplying the omission. 



I am very strongly of opinion that every description of a new 

 Rotifer should be accompanied by a good figure, because a drawing 

 gives a much better idea of the creature, and is always re- 

 membered, whilst a description without figure is usually lost 

 sight of and forgotten. 



According to Skorikow's description, the three long, thin and 

 curved appendages, two lateral and one posterior, are movable, 

 in the same way as are the two small lateral spines in JVotholca 

 sjnnifera ; but farther on the author states that he has not seen 

 the posterior spine move, so there appears to be uncertainty as 

 to whether the posterior appendage is really capable of move- 

 ment, which I much doubt. 



By means of the spines the animal is said to be capable of 

 jerky forward movements in the manner of a Triarthra. 



The lorica is very thin, resembling in this respect the marine 

 plankton forms ; it is oval in shape, with a high and rounded 



* " BeobachtaEgen fiber das Plankton der Newa," Biol. Centralhlatt. xxv. 

 1905, pp. 1-19. 

 JouRN. Q. M. C, Series II. No. 70. 25 



