PTEROD1NA. 



177 



fresh and brackish water : it has a smooth lorica, 

 round at the base, and six short spines in front ; it 

 is nearly as large as Noteus quadricornis. B. ru- 

 bens is similar in shape, but the body is reddish. 

 Pterodina patina (Drop IV. fig. 16). This is 

 one of the most delicate, beautiful, and transpa- 

 rent of these lovely little beings. When viewed 

 with a magnifying power of 250 diameters, it 

 appears about the size of a sixpence, the lorica 

 nearly round, and having no processes like the 

 other genera of this family : it is exceedingly 

 flat, and so transparent that, with the exception 

 of some parts of the body, it is difficult to see this 

 animalcule if the water is very clear. The ro- 

 tatory organ is double, forming two wheels ; the 

 tail, or foot, is thick, rather clumsy, and furnished 



