98 AVIAN ENLTOZOA—LINTON. 
Distomum flexum sp. noy. 
(Pl. vi, Figs. 36-44.) 
It has been found necessary to nake a new specific name to accom. — 
modate a small Distomum from the black scoter (Oedemia americana), 
although its near relationship to at least two described forms is quite © 
evident. It agrees very closely with Diesing’s D. baculus; indeed, if 
Diesing’s description alone were employed it could be readily referred 
to that species. Von Linstow, however, in his account of D. baculus 
(Trosh. Archiv. 1877, p.183, Pl. x11, Fig. 15), neither mentions nor fig- 
ures any cervical spines. It is not at all probable that such a careful 
observer as he would neglect to mention such an important character, 
especially as in his figure of D. spinulosum (|. c. Fig. 14), the cervical 
spines are shown. The latter species must be excluded on account of © 
the smaller number (twenty-two) of the oral spines. 
A Distomum discovered and described by Olsson from Larus marinus, 
and called by him D. pseudoechinatum (Bitrag till Skandinaviens Hel- 
minthfauna, p. 21, Pl. Iv, Figs. 45-49) resembles my specimen in the 
spinous margins of the neck and in the general appearance of the head. 
It is much larger, however, being 8 millimeters in length, and has, 
moreover, only about twenty oral spines. 
The body of this specimen is subeylindrical and linear; the neck is 
attenuate anteriorly, concave on the ventral side, just back of the 
head, and armed with spines along the margins; the head is trans- 
versely reniform and provided with a crown of about forty-five spines; 
the mouth is terminal and prominent, its aperture circular ; the ventral 
sucker is about twice the diameter of the mouth and sessile; pharnyx 
elongated ; genital aperture in front of ventral sucker; testes two, 
oval, midway between ventral sucker and posterior eud; ova few and 
large. 
Length, 2.5 millimeters. 
Other dimensions are: 
Millimetere. 
Diameter of head: 2... 22 S55. ceos cose emeen’ ooeteet eee Seem 30 
Diameter ot neck .-. S20) f.4s2 2c Pa se sie ee eee 19 
Diameter of the body at the ventral sucker...--...---.---- .40 
Diameter of body near posterior end....--...--.....--.---- .26 
Diameter of ventral sucker, internal 2-2... en oess saseoe eee 16 
Diameter of ventral sucker, extermal-...... ....-..-.--.-.-5 ~ 28 
Diameteriof oral sucker; internallss--- 4-2 seen see eee 
Dixmeter of oral ‘sucker, external.Gs. 2... o.eee eens soe ee ome es 
Lengthof testes’... 22% '2: Jago. ce Bete on ese tee eee say 20U 
The oral hooks are flat and broad, aud the larger ones 0.0535 milli- | 
meter in length, and 0.01 to 0.015 millimeter in breadth. 
The cervical spines are triangular and 0.015 to 0.02 millimeter in 
length. These spines appeared to be only in the margins of the neck, | 
although possibly they may extend dorsally for a short distance. 
The front edge of the ventral sucker was 0.5 millimeter from the an- 
. 
