118 Monograpli of the. Crustacea of the Cincinnati Groujy. 



their characters ; they include a vast number of the most minute Crus- 

 tacea known ; ail those inclosed in a Ijivalve, shell-like carapace (an 

 extension of one of the cephalic rings) belong to it. They have no 

 -gills, but breathe by flat, membranaceous, vascular vesicles, attached to 

 the thoracic extremities, and representing the flabelliform appendage 

 and palpi thereof, modified for the purpose, or by the surface of the 

 body only. The eyes, whether simple or comjDound, are covered by a 

 smooth cornea. This order, which is of more importance to the geolo- 

 gist than all the rest of the class, is divisible into three tribes, named 

 according to the structure of the feet : 1st, Phylhpoda ; 2d, Pcecilopoda ; 

 3d, Loj)hyropoda. 



First Tribe — Phyllopoda. 



These have the feet extremely numerous, and, as their name implies, 

 all leaf-shaped. They form extremely numerous, thin, membraneous 

 lobes, subservient, to respiration. The tribe is divisible into the fol- 

 lowing families: 1st, Lymnadiadce ; 2d, LeperditidK ; 3d, Apodiadce; 

 4th, Trilobltadce; 5tl», Branchipodiadae; 6th, Dapliniada (or Cladocera). 



Family Lymnadiadce — (McCoy). 



Body entirely inclosed in a vertical, bivalve, calcareo-corneous, ob- 

 long carapace, opening along the ventral margin; head adhering to the 

 carapace ; twenty to thirty pair of membraneous, respiratory feet ; two 

 eyes, either united in one central mass or separate, one soldered to each 

 valve. 



The t}^-)e of this family is the recent genus Lymnadiadce. It is made 

 to include, however, the genera Beyrichia, Cythere, etc. 



Genus Beyrichia — (McCoy, 1855). 



" Bivalve, rotundato-quadrate or longitudinally oblong, ends un- 

 equal ; anterior, posterior, and dorsal margins convex, and surrounded 

 by a sharply defined, narrow, tumid border or rim; ventral margin 

 simple, straight or concave ; sides tumid, strongly divided into lobes 

 by very deep, nearly vertical furrows, extending from the ventral more 

 or less towai'd the dorsal margin." 



'to' 



Beyrichia- Oculifer — (Hall, 1871). 

 Carapace small, seldom exceeding 7-100 of an inch in length, by 



