555 



septa serve this purpose. Not iiilreiiiieiUly, and especially in the an- 

 terior part of the worm, there is a considerahle lack of correspondence 

 in the external and internal honndaries of somites thus indicated. 

 Septa and interseji^mental grooves for any two somites are repre- 

 sented hy the same formula — for example, \^/VI— the context show- 

 ing which is meant. In all of our species except a few found in green- 

 houses there are 1)ut eight set^c per somite, and these are more com- 

 monly arranged in pairs. It is customary to indicate the seta: of 

 either side hy the use of the letters a, b, c, and (/, the ventral-most 

 seta heing designated hy a, the next hy h, the next hy c, and the dorsal- 

 most one hy d. If the distances ah and cd are less than one third of 

 the distance be, the seta: are said to he closely paired, and if otherwise, 

 they are widely paired. The clitellum may he incomplete ventrally or, 

 in some species of Diplocardia, it may he nearly as thick on the ven- 

 tral surface as elsewhere. In the accompanying tahle the former con- 

 dition is denoted by the term saddle and the latter by cingulum. Tu- 

 bercula pubertatis are glandular ridges closely associated with the 

 ventral edges of the clitellum on some of its somites. 



The spermatheca: are pouches which open to the exterior and 

 receive sperm cells from another individual. They are the same as 

 the seminal receptacles mentioned in many text-books. The sperm 

 sacs open into the cavity of X or XI and store temporarily the sperm 

 cells produced in those somites. Each sperm sac lies in a somite ad- 

 jacent to the one into which it opens. These organs are often called 

 seminal vesicles in the text-books. The prostate glands are not found 

 in the Liimbricidcc and hence are not ordinarily mentioned in the text- 

 books. They are large glands more or less closely associated with the 

 external openings of the sperm ducts, and in indigenous Illinois spe- 

 cies open separately (prostate pores) from them on neighboring so- 

 mites. 



The foregoing key includes .all but two of the described species 

 of which representatives have been collected in Illinois, and gives the 

 main characters necessary for their identification. Because of the 

 large number of species in the genus Phcrctima and the consequent 

 difficultv in determining them, P. Jictcrochacta and P. haivayana are 

 not included in the key. Acklitional matter concerning distribution 

 and habitats is included in the following text, as are also, in brackets, 

 citations to descri])tions of most of the species. 



Diplocardia riparia Smitli (PI. XLI, Fig. TO-12). — [Smith, 'Q5a : 

 138.] Abundant in the rich soil of the l)ottoni-land forests of the Illi- 

 nois and the Kaskaskia rivers. 



