2O EISEN 



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



posteriorly emarginated. About 6 globular atrial glands. Lympho- 

 , cytes 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 posteriorly. Two atrial 

 glands. Lymphocytes ellipsoidal, without fringes. 



24. M. eastivoodi 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. primcevus Eisen, '79. 



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



than the stalk. Brain posteriorly narrower than anteriorly, slightly 

 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. beumeri 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. No atrial glands but accessory glands present in connection tvith lower 



apex of the penial bulb ; penial glands in Denial 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 lower 



apex of sperm-ducts. 

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



29. M. pedatus sp. nov. 



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



penial glands inside the bulb. 



Brain slightly rounded, tapering posteriorly. Spermathecse with enlarged 

 pouch opening into the intestine 30. M. 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 (Emery, '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. 



MESENCHYTR^US UNALASK/E sp. nov. 



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



Definition. Length 5 mm., width .4 mm. Somites about 40. 

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

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

 4> 3 4. 4i 3> etc -> 3i 2 J ventral, 7, 7, 7, 7, 7, etc., o (XII), 6, 5, 5, 

 4, 5, 4, etc. Setae in ventral fascicles diminish in size toward ventral 

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

 prominent but not pointed. Clitellum unknown. Sexual papilla- not 

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

 deeply emarginated. Dorsal vessel rises about XVIII. Intestine 



