20 EISEN 



3. Diverticles shorter than the ampulla of spermatheca. Brain broad, 



posteriorlj emarginated. About 6 globular atrial glands. Ljmpho- 

 cjtes ellipsoidal, fringed. Length about 15 mm. 



23. M. fuscus sp. nov. 



4. Diverticles about equal in length to the stalk as well as to the am- 



pulla of spermatheca. Brain square, truncate posteriorlj. Two atrial 

 glands. Lymphocytes ellipsoidal, without fringes. 



24. M. easivjoodi sp. nov. 



5. Diverticles simple, slightly shorter than the ampulla of spermatheca. 



Sperm-duct about equal in length to the funnel. Brain broad, 

 slightly emarginated posteriorly 25. M. primcBVus Eisen, '79. 



6. Diverticles broader than the ampulla but about as long; shorter 



than the stalk. Brain posteriorly narrower than anteriorly, slightlj' 

 emarginated. Head-pore anterior to the center of prostomium. 

 Sperm-duct about 8 times as long as funnel. Lymphocytes ellip- 

 soidal, almost circular 26. M. ^e«we/V Michaelsen, '86. 



7. Diverticles form merely a central chamber between the duct and the am- 



pulla, in which the paired nature of the diverticles is barely percep- 

 tible. No specialized sperm-duct, the narrow part of the funnel serv- 

 ing for duct and opening directly into the pore. Brain posteriorly 

 deeply emarginated 27. M. nanus sp. nov. 



c. N'o atrial fflattds but accessory glands f resent in connection luit/t lower 



apex of the fenial bulb ; fenial glands in fenial bulb. 

 Brain posteriorly slightly emarginated. Two small club-shaped diver- 

 ticles at the center of the spermatheca 28. M. fontinalis sp. nov. 



d. No atrial and no ■penial glands, but many accessory glands at the loxver 



apex of spertn-ducts. 

 Brain truncate. Large penial projection of the body-wall. 



29. M. fcdatus sp. nov. 



e. No atrial glands. No accessory glands at the male-pore, but ma7iy large 



penial glands i?iside the bulb. 

 Brain slightly rounded, tapering posteriorly. Spermathecae with enlarged 

 pouch opening into the intestine 30. AI. beringensis sp. nov. 



IV. Spermatheca with three diverticles. 



Brain truncate posteriorly. Atrial glands 6 or more. Numerous accessory 

 glands opening exterior to penial bulb. Penial glands in the bulb trefoil- 

 like 31. M. solifugus {Y.mery, '98). 



V. Spermatheca with 4 or 5 globular diverticles at the base of the 



AMPULLA. 



Spermatheca turret-like. Sperm-ducts very short and broad. Body intensely 

 blackish brown 32. M. mirabilus Eisen, '79. 



MESENCHYTIL^US UNALASK^ sp. nov. 

 p1. I, fig. 7; and text-fig. i. 

 Definitio?i. — Length 5 mm., width .4 mm. Somites about 40. 

 Anterior four somites thicker than those following. Somites I to III 

 rugose and warty. Sets : lateral, 4, 4, 4, 3, 3, 3, 2, 3, 3 (XII), 2, 3, 

 4» 3' A-> 4^ 3^ etc, 3, 2 ; ventral, 7, 7, 7, 7, 7, etc., o (XII), 6, 5, 5, 

 4, 5, 4, etc Sctte in ventral fascicles diminish in size toward ventral 

 interval ; setas in lateral fascicles of about equal size. Prostomium 

 prominent but not pointed. Clitellum unknown. Sexual papillae not 

 projecting. Septal glands large, in IV to VI. Brain posteriorly 

 deeply emarginated. Dorsal vessel rises about XVIII. Intestine 



