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larger than hooks of remaining circles. Terminal hooks 41 » long; hooks 
of middle circle 32 to 35 »; those of basal circle 24 to 30 pw. Testes ellip- 
tical, not crowded together. Sperm ducts of mature males frequently 
showing a number of vesicular enlargements between the posterior margin 
of anterior testis and the anterior margin of the cement-gland. Cement 
gland not in close contact with posterior testis, frequently broadly sepa- 
rated from it; form typical of the family, containing eight giant nuclei. 
Embryos within body-cavity of mature females 30 to 47 » long by 15 to 
18 p wide. 
Type host, Catostomus commersonii (Lacép.); type locality, Douglas 
Lake, Michigan. 
Cotypes deposited in the U. S. National Museum and in the collec- 
tions of G. R. La Rue and of H. J. Van Cleave. The material from which 
this species was described was collected by Dr. George R. La Rue in July 
and August, 1912. 
GRACILISENTIS, n. gen. 
Neoechinorhynchus, in part; ( = Neorhynchus = Eorhynchus). 
Generic Diagnosis —Neoechinorhynchidae of small size, parasitic in 
the digestive tract of fishes. Body proper unarmed. Proboscis provided 
with three circles of twelve hooks each. Each thorn ensheathed in a 
prominent cuticular collar which permits only a small portion of the thorn 
to protrude from the surface of the proboscis. Each hook of the terminal 
circle provided with a conspicuous root-process several times longer than 
the exposed portion of the spine. Root composed of a broad flat basal 
area which, by gradual diminution in size anteriorly, makes an ill-defined 
transition from thorn to root. Basal region of terminal roots frequently 
slightly indented. Hooks of middle circle similar in general form to those 
of terminal circle except that root processes are shorter and less easily 
observed. Basal hooks without recurved roots. 
Type species, Gracilisentis gracilisentis (Van Cleave, 1913). 
GRACILISENTIS GRACILISENTIS (Van Cleave, 1913) 
(Pl. XXVII, Fig. 30, 31, 32) 
Body small, tapering slightly at either extremity; extremities bent 
toward ventral surface, forming a slight crescent. Fully mature females 
1.7 to 4 mm. long, greatest diameter slightly anterior to middle of body, 
0.38 mm. Males 1.5 to 3 mm. long, greatest diameter 0.38 mm. Proboscis 
approximately pear-shaped, usually with a slight constriction between 
the middle and basal circles of hooks. All hooks very delicate; those of 
terminal circle 15 to 17 p long, with a root 20 »; those of second circle 12 
to 15 », with root about 15 » long; those of basal circle almost straight, 
15 to 20 » long, without root. Cement gland containing eight giant nuclei. 
Embryos conspicuously spindle-shaped 36 to 40 » long by 10 » broad. 
Type host, Dorosoma cepedianum (LeS.) ; type locality, IWinois River 
at Havana, Illinois. 
