101 Insects. 



ers. The organs of mastication are not however the only organs that 

 are worthy of being noticed. The beautiful and delicate structure of 

 their feet and branchial appendages are worthy of all admiration. 

 These latter organs are almost constantly in motion, and present a 

 most interesting appearance when viewed under the microscope. The 

 extraordinary method they have of reproducing their young, with the 

 transformations which some of them undergo in an early stage, are 

 subjects which might occupy a considerable time in describing, and 

 which cannot be attended to without exciting the greatest interest in 

 the mind of the observer. A full and most interesting account of these 

 curious matters may be seen in Jurine's work on the Monoculi found 

 in the neighbourhood of Geneva, and in a series of papers published 

 in the 'Magazine of Zoology and Botany' for 1836-7. 



The least known of all the genera of this interesting order of crea- 

 tures is the genus Cythere. It was established by Muller, in his 

 * Zoolog. Dan. Prod.' in 1776, and several species were afterwards de- 

 scribed by him in his ' Entomostraca,' in 1781. The whole of these 

 were marine, and no other author, after Muller, seems to have taken 

 any notice of them, either with regard to their anatomical structure, 

 or extending the number of species. Nestling in the quiet secluded 

 little pools in the rocks on the sea-shore, amongst the little corallines 

 and sea-weeds which make their abode there, they were very likely to 

 escape the notice of most naturalists ; and accordingly, as far as I 

 know, no new recent marine species had been described since Muller's 

 time, till I described several in the ' Transactions of the Berwickshire 

 Naturalists' Club ' for 1835 ; and afterwards in the ' Magazine of Zo- 

 ology and Botany,' in 1836 : where also I have described all that is 

 yet known of the anatomical structure of these curious little creatures. 



In 1817, Say, in a paper published by him in the * Journal of the 

 Academy of Natural Sciences of Philadelphia,' on the Crustacea of the 

 United States, recorded a species as found in fresh water in Georgia 

 and East Florida, and we believe that till now it was the only recent 

 fresh-water species that had been discovered. In the * Transactions 

 of the Geological Society,' v. 136, Mr. Sowerby describes a fossil spe- 

 cies from Hampstead; but there is so little difference in the shell be- 

 tween this genus and Cypris, that it appears to me very difficult to be 

 able to refer a fossil species to the genus. In the autumn of 1841 I 

 discovered the species here described, in a pond of fresh water near 

 Hanwcll, in Middlesex, being the second fresh-water species yet re- 

 corded. 



