Entozoa from the Murman Coast. 509 
while it is readily distinguished from M. macracanthum, 
Fuhrm., by the much smaller size of its hooks. Both these 
species occur in closely related hosts. 
Monopylidium stercorarium, sp. n. (Figs. 5-7.) 
Host: Stercorarius pomarinus (pomatorhine skua). Yu- 
kanski, 22. vi. 1917. 
This is a comparatively short worm, measuring 2°5-3 em. 
in length. The maximum width is about 0°38 mm, (near the 
posterior end). ‘The number of segments is rather small 
(about ninety). 
Fie, 5. Tie, 6. 
Hs ~ ) SOu 
Fig. 5.—Monopylidium stercorarium; the scolex. 
Fig. 6.—Ditto ; hook from the rostellum. 
The scolex (fig. 5) measures about 0°4 mm. across, and the 
suckers are 0°18 mm, in diameter. The rostellum is rather 
long and stout, and is armed with a single crown of 
fourteen (?) very large hooks, 110 yw in length (fig. 6). The 
long roots of the hooks meet at the apex of the rostellum. 
Segmentation begins immediately behind the scolex. The 
anterior segments are broader than long; soon, however, they 
become squarish, and posteriorly they are much longer than 
broad. Rudiments of genital organs begin to appear at 
