842 



FRESH-WATER BIOLOGY 



9 (8) Eyes wanting. Head not narrower than the first thoracic segment. 



Telson much longer than broad. . . Caecidotea Packard. 

 Four species, in caves, springs issuing from caves, and artesian wells. 



10 (5) Pleopods not covered by an opercular plate. Body of female pecu- 



liarly deformed, unsymmetrical, that of the male more or 

 less normal and symmetrical. Parasitic upon higher crus- 

 taceans Family Bopyridae. 



Only one genus in the North American fresh waters. 



Probopyrus Giard and Bonnier. 



Chiefly a marine group; the only genus 

 known from the fresh water of North 

 America, enters with its hosts, being found 

 parasitic upon the gills and in the gill cav- 

 ities of Decapods of the genera Palacmo- 

 netes and Palaemon. Three species are 

 known, and are found along the Atlantic 

 coast from New Hamsphire to Florida, and 

 in the Mississippi River in Louisiana. 



Fig. 1306. Probopyrus pandalicola Packard. A, 

 Male; X 30. B, Female; X 3. (After Richard- 

 son.) 



II (2) Body compressed. Pleopods divided into two sets, the first three 

 pairs with multiarticulate rami, the last two pairs generally 

 similar to the uropods, with unsegmented rami. No sexual 

 modification of pleopods in the male. 



Order Amphipoda . . 12 



12(25) Antennulae with secondary flagellum. Telson clef t or entire. . . 13 



13 (14) Fifth peraeopods shorter than the preceding. Second maxillipeds 

 smaller than the first. Uropods with two nearly equal 



rami Family Lysianassidae. 



Only one fresh-water genus in North America. . Pontoporeia Kroyer. 



This family is chiefly marine; two spe- 

 cies live in rather deep wafer of the lakes 

 Superior and Michigan. These species 

 are closely allied to certain European 

 fresh-water forms, and probably immi- 

 grated into the lakes at the close of the 

 glacial time. 



Fig. 1307. Pontoporeia hoyi Smith. X 4. 

 (After Smith.) 



14 (13) Fifth peraeopods longer than the preceding. Second maxillipeds 



generally larger than the first. Uropods with two unequal 

 rami or without rami. . . . Family Gammaridae. . 15 

 A family represented both in the sea and in fresh water, and containing a great number of 

 forms. 



15 (20) Telson cleft. Uropods biramous 16 



16 (19) Inner ramus of uropods rudimentary. Telson cleft not more than 



three-fourths the distance to the base 17 



