Apr. i, 1925 New Nematodesfrom North American Mammals 
679 
NEMATODES FROM BEAVER 
Travassosius americanus, n. sp. 
Male: 11 mm. long, slender, 96 fx in 
diameter at the level of the esophage- 
intestinal valve, diameter increases 
evenly to 116 m at a point just in front 
of the prebursal papillae. Head small, 
30 ix in diameter, buccal capsule absent, 
esophagus 575 n long; its greatest 
diameter is 65 n near the posterior end. 
Nerve ring surrounds esophagus at a 
plane 260 ix behind the anterior end. 
The excretory pore is about 345 ix from 
the head. The cervical papillae are 
large, conical, and prominent, about 
50 fx behind the excretory pore. The 
prebursal papillae are lateral, 50 m in 
front of the anterior margin of the 
bursa. The bursa is in most respects 
similar to that of T. rufus Khalil. 4 
The most conspicuous difference is in 
long by 60 n in diameter. The eggs 
are oval, thin shelled, from 82 to 90 jx 
in length by 43 to 50 fx in width. 
Habitat: In stomach of Castor can¬ 
adensis , National Zoological Park, 
Washington, D. C., January 23, 1924; 
E. A. Chapin collector. 
Type: United States National Mu¬ 
seum, Helminthological Collections, 
No. 25966, paratypes No. 26107. 
Paratypes also deposited in the British 
Museum (Natural History). 
This species is very closely related to 
T. rufus Khalil, the type of the genus. 
The spicules are smaller in the present 
species and are somewhat different in 
conformation. 
Castorstrongylus n. gen. 
Strongylidae, Strongylinae, Cylicos- 
tomeae. Medium-sized worms, sexes 
of approximately the same size. Buccal 
Fig. 2 .—Ostertagia bisonis, n. sp. A, bursa of male from side; B , same, ventral view; C, spicules 
the formation of the dorsal ray, which 
bifurcates at a point 56 fx from the 
base of the ray and produces two 
branches, each 16 fx neither of which 
bifurcates at the extremity. The 
spicules are two, and similar, from 148 to 
152 ix long. Gubernaculum is absent. 
Female: 12 mm. long; diameter of 
head 30 /x, greatest diameter 128 fx , 
near vulva. Esophagus about 600 /x 
long, nerve ring 280 /x behind its an¬ 
terior end. Excretory pore 430 jx, 
cervical papillae 460 /x from anterior 
end. Vulva about 3 mm. from the tip 
of the tail. Tail slender, slightly re¬ 
curved at its tip, anus 240 /x from the 
tip. The length of the combined 
portions of the ovejectors, including the 
sphincter muscles is about 630 /x; 
each sphincter alone measures 45 \x 
capsule large, heavily walled, without 
teeth at base. External corona of 
fimbriated elements, internal corona of 
short, stout peglike elements. Cervical 
papillae and excretory pore a short 
distance apart, both behind the nerve 
ring. Bursa of male moderate. Ven¬ 
tral rays close together and parallel, 
externo-dorsal arising free of the trunk 
of the dorsal, dorsal twice bifurcated. 
Vulva near anus, uteri directed ante¬ 
riorly, convergent. 
Habitat: In colon of a rodent. 
Type and only known species: 
Castorstrongylus castoris n. sp. 
The type species has the habitus of a 
true Strongylus while the bursal and 
other characters usually chosen as of 
tribal importance place it in the neigh¬ 
borhood of the cylicostomes. 
* Khalil, M. travassosius rufus, gen. et sp. n.: a nematode (trichostrongylidae) parasitic 
in the stomach of the Norwegian beaver, Ann. and Mag. Nat. Hist., 10: 281-289, illus. 1922. 
