IV. 



MUD-INHABITING CRUSTACEA. 



Plate IX. 



Among the curiosities of pond life are certain minute crustaceans 

 which spend their entire Hfe in the soft debris and mud forming the 

 superficial deposit at the bottom. The Canthocamptus among cope- 

 pods is commonly found in such situations, but this is less surprising 

 than that members of the cladocera, or shelled entomostraca, with their 

 delicate organization and frail structure should have become adapted 

 to such a life. In many marine crustaceans (copepoda) the accomo- 

 dation to such a reclusive life is manifested in the retrograde devel- 

 opment of many of the organs — eyes, even, being absent in several 

 cases. The present paper is concerned only with a few cladocera, 

 which are peculiar to America or rare both here and elsewhere, and 

 which exhibit curious and instructive modifications as a result of such 

 a habitat. The reader who wishes to familiarize himself with the sys- 

 tematic classification of the group would do well to consult Die Clado- 

 ceixn Boehmens, by Hellich, Birge's Notes on Cladocera, and the 

 writer's Final Report o?t Crustacea of Minnesota, while, for a thor- 

 ough study of the physiology, Weisman's Beitraege zur Naturgeschiclite 

 der Daphnoiden, is necessary. A special paper on the limicole or 

 mud-loving cladocera was published in the Zeitschrift fuer Wissenchaft- 

 liche Zoologie, in 1S78, by Dr. Wm. Kurz, and entitled Ueber li??ii- 

 cole cladoceren. Reference will be frequently made to this paper and 

 this must be understood in all cases of reference to Kurz, unless other- 

 wise specified. These mud-dwellers are happily called ^'- schmutz-pe- 

 terchen'^ cladocera, i. e. "Smut-Johnny," or chimney-sweep water 

 fleas. In America the following species are pre-eminently worthy of 

 the name : Monospilus tenuijvstris, Leydigia quadrangida?'is , Alona 

 sanguinea, Alona quadrangula, Plcuroxus procurviis, and several other 

 members of the genera Alona and Pleuroxus. The typical cladocera 



