236 
two layers of muscle inserted at the base of the proboscis. Central 
nervous-system near the middle of the proboscis receptacle. 
ECHINORHYNCHUS THECATUS Linton, 1891 
(Pl. XXII, Fig. 1-4) 
Length: females, 11 to 26 mm.; males, 7 to 12 mm. In fully extended 
individuals both ends of the body are bent toward the ventral surface. 
Proboscis, when fully extended, frequently takes a position perpendicular 
to the axis of the body; in case of extreme extrusion may form acute 
angle with main axis of body. Proboscis usually about 1 mm. long. Neck 
about one-fourth the length of proboscis. Proboscis receptacle long and 
slender, about 1.5 times the length of proboscis. Central nervous-system 
located near the center of the proboscis-receptacle. Hooks alternate in 
arrangement; restricted entirely to proboscis; arranged in twelve longi- 
tudinal rows of twelve to thirteen hooks each. Lemnisci long and slender, 
about 1.5 times the length of proboscis-receptacle. Embryos within body- 
cavity of gravid female 80 to 110 » long by 24 to 30 » wide. The hooks 
at the base of the proboscis are 41 to 53 » long, nearly straight, and in 
many instances each hook is completely ensheathed in a cuticular collar 
(Fig. 2). Near the middle of the proboscis, hooks of a much heavier 
form occur. These are rather uniformly about 71 » long, although those 
on the ventral surface of the proboscis are more strongly curved and a 
little heavier than those on the dorsal (Fig. 2, 4). Hooks near the ante- 
rior tip are not so much recurved and not so strong as those near the 
middle though they reach greater length; namely, 77 to 89 p. In the 
male eight cement glands are closely compacted at the posterior border 
of the hind testis. 
Graybill (1902 :197) has given a very good description of this 
species, from which the foregoing data vary but slightly. 
Hosts: Morone americana, Roccus americanus, Micropterus dolo- 
mieu, M. salmoides, Ambloplites rupestris, Amia calva, Lepisosteus pla- 
tostomus, Hiodon tergisus, Ictiobus bubalus, Carpiodes carpio, Cyprinus 
carpio, Ictalurus punctatus, Pomoxis annularis, P. sparoides, Lepomis 
pallidus, Eupomotis gibbosus, Perca flavescens. 
ECHINORHYNCHUS SALVELINI Linkins, 1918 (in Ward and Whipple) 
(Pl. XXIII, XXIV, Fig. 5, 10, 12) 
Body slightly enlarged anteriorly. Males 7 to 9 mm. long; 0.82 to 
1.27 mm.in maximum diameter. Females 10 to 17 mm. long; 1.2 to 1.6 
mm. in maximum diameter. Proboscis cylindrical, armed with 16 longi- 
tudinal rows of about 13 hooks each. Basal hooks 39 to 50 » long. Hooks 
on middle and anterior proboscis-regions 44 to 68 » long, with basal pro- 
cess 83 » long. Embryos 115 to 165 » long by 20 to 25 « broad; middle 
