Entozoa from the Murmun Coast. 



509 



wliilo it is readily distitjf^uisliod from }f. macmranthum, 

 Fulirm., l»y the luiicli smaller size of its hooks. Bolli these 

 species occur in closely related hosts. 



Monopylidium stercorarium, sp. n. (Figs. 5-7.) 



Host: Stercorarius f^marinux (pomatorhiiie skua). Yu- 

 kanski, 22. vi. 1917. 



This is a comparatively sliort worm, measuring 2*5-3 cm. 

 in length. The maximum width is about Q'S mm. (near the 

 posterior end). The number of segments is rather small 

 (about ninety). 



Fit 





ri^. <i 



50// 



Fig. 5. — Monopylidium ttercorariunt ; the scolex. 

 Fig. 6. — Ditto ; hook from the roattiilum. 



Tb« scolex (fig. 5) measures about 0*4 mm. across, and the 

 suckers are 0"18 mm. in diameter. The rostelltmi is rather 

 long and stout, and in armed with a single crown of 

 fourteen (?) very large hooks, 110 ^ in length (tig. 6). The 

 long roots of the hooks meet at the apex of the rostellum. 



iSegmentation begins immediately behind the scolex. The 

 anterior segments are broader than long; soon, however, thev 

 become squarish, and posteriorly they are much longer than 

 broad. Rudiments of genital organs begin to appear at 



