EISEN 



Locality. Found at Goose Lake, Alturas and other localities in 

 Modoc County, California. Collected by Dr. Richard C. McGregor. 

 Probably common in the mud of creeks and lakes in the Sierra Nevada 

 region of northern California. 



Characteristics. Readily distinguished exteriorly by very large 

 copulatory papillae in XII, especially in specimens where they are fully 

 extended, the papillae then being as long as the diameter of the body. 

 Interiorly it is prominently characterized by the enormously large 

 accessory glands, which open in the immediate vicinity of the sperm- 

 ducts (pi. ix, fig. 5). 



DETAILED DESCRIPTION. 



Seta. In the first few somites the number of setae varies between 

 three and four in the lateral fascicles, while in the ventral fascicles we 



find six setae in 

 the three anterior 

 fascicles and five 

 in the following. 

 Posterior to cli- 

 tellum the setae in 

 the ventral rows 

 are unif o r m 1 y 

 five, while in the 

 lateral rows they 

 are only four. All 

 the setae in the 

 same fascicle are 

 of about the same 

 size. 



Head- pore. 

 This pore is situ- 



FIG. 30. Mesenchytr&us pedatus. 



ated (fig. 29, a} a little in front of the shallow groove which separates 

 prostomium from somite I. 



Spermiducal apparatus (pi. ix, figs. 4 and 5). As stated, the 

 large sexual papilla is most conspicuous. When fully extended its 

 long diameter is equal to the diameter of the body at somite XII 

 (pi. ix, fig. 5). The sperm-ducts open at the apex, and this latter is 

 surrounded by the elevated margin of the body-wall, here consisting of 

 large broad cells. Surrounding the opening of the sperm-ducts is a 

 small bulb, into which opens a ring of very large accessory glands. 

 These glands extend inward to the center of the body-cavity. Their 

 structure seems to resemble that of the septal glands. The sperm- 



