550 FRESH-WATER BIOLOGY 



27 (12) Hooks not alike on ventral and dorsal surfaces of proboscis. . . 28 



28 (29) Hooks differ in form, especially of root, but not in size. Body uni- 



formly cylindrical or nearly so. 



Rhadinorhynchus Liihe 1911. 



Hooks of dorsal surface with much shorter root, also slenderer and less curved than those on 

 ventral surface. In marine fishes almost exclusively, but present in trout from eastern states. 

 Species yet undescribed. 



29 (28) Hooks differ noticeably both in form and size. Body very large 



and slender, with marked enlargement near anterior end. 



Arhythmorhynchus Liihe 1911 . . 30 



Body in front of enlargement covered with fine spines. Proboscis very long, enlarged at 

 center, oblique to body axis. Adults in intestine of birds. 



30 (31) Hooks on mid-ventral surface of proboscis conspicuously larger 



than any others. 



Arhythmorhynchus trichocephalus (R. Leuckart) 1893. 



Body very slender. Length 5 to 8 cm., diameter 0.5 to 0.8 mm. Ovoid swelling 2.3 to 2.9 

 mm. behind neck with length of 1.6 to 2.4 mm. and breadth of 0.6 to 1.4 mm. Anterior to 

 swelling many dermal spines 28 to 35 p long. Proboscis with 20 longitudinal rows and 19 or 

 20 transverse rows of hooks. 



From Florida; host unknown. 



31 (30) Hooks on mid- ventral surface of proboscis not conspicuously larger 



than others 32 



32 (33) Large hooks exceed 100 /* in length. 



Arhythmorhynchus uncinatus (Kaiser) 1893. 



Length 4 to 6 cm., diameter i to 1.2 mm. Ovoid swelling about 5 mm. behind neck; 0.6 

 mm. in front of swelling prominent annular enlargement i to 1.4 mm. long, 1.7 to 2 mm. in 

 diameter and covered thickly with small spines. Proboscis with 18 transverse and 18 longi- 

 tudinal rows of hooks. 



From Florida; host unknown. 



33(32) Large hooks not more than 50 /* long 34 



34 (35) Eighteen longitudinal rows of hooks. 



Arhythmorhynchus brevis Van Cleave 1916. 



Female 6 to 12 mm. long, 3 mm. wide. Male 5 to 6 mm. 

 long, i to 1.5 mm. wide. Neck naked. Body just back of 

 neck with few small spines. Proboscis 0.665 mm. long, 0.23 

 mm. wide at base, 0.19 mm. at tip, 0.34 mm. at center. Em- 

 bryos 76 to 100 n by 24 to 30 IJL. Middle shell heavy, with 

 rounded swelling at each pole. 



From bittern (Botaurus lentiginosus); Baltimore, Mary- 

 land. 



FIG. 854. Arhythmorhynchus brevis. Anterior end of body. X 40. 

 {After Van Cleave.) 



