24 



Notes on Some Little- Known Species of Pterodina. 

 By Charles F. Rousselet, F.KM.S. 



{Read January 2lst, 1898.) 

 Plates 3, 4, 5. 



The interesting group of oval or nearly circular and flat 

 Rotifers of which Pterodina 2^citi^ici is the type, has always been 

 admired by microscopists on account of its peculiar beauty, the 

 glassy carapace, when reflecting the light under a good dark 

 ground illumination, resembling a bright new silver coin more 

 than anything else. Pastor Eichhorn w^as perhaps the first to 

 discover, figure and describe a member of this group, in 1781, 

 followed soon after, in 1786, by 0. P. Miiller, who speaks of it as 

 " Animalculum crystallinum splendore nulli secundum," and so it 

 is to-day. 



Seven species have been mentioned by Dr. Hudson in his great 

 work, but since then six or seven more species have been added to 

 the list, making thirteen or fourteen species in all that are now 

 known, as follow^s : — 



Pterodina patina Ehrbg. Pterodina bidentata Ternetz 



„ valvata Hud. ( = Pt. emarginata Wierz). 



„ clypeata Ehrbg. Pterodina coeca Parsons. 



. „ elliptica „ ,, trilobata Shephard. 



„ mucronata Gosse. „ intermedia Ander- 



„ reflexa Gosse. son, 



„ truncata „ „ crassa Levander ( = 



„ parva Ternetz. Pt. clypeata). 



,, incisa „ 



It is not the object of this paper to pass in review all these 

 species, but only to describe four or five of them which have come 

 under my observation, and which, owing to insuflicient figures, 

 are somewhat difiicult of identification. 



One of the principal charactei^ of the genus, as defined by 



