204 W. B. BENHAM. 



two setse placed close to one another; and in place of the 

 terms " dorsal " and '' ventral " setse I shall employ the 

 words " outer " and " inner " in describing the couples in 

 reference to their position relative to the ventral mid-line of 

 the body. When the eight setae become wider and wider 

 apart it sometimes becomes advisable to speak of such setse as 

 being " separated/' 



The four setae on each side may be termed, with Perrier,^ 

 1, 2, 3, 4; the first being most ventrally placed, the fourth 

 most dorsally. 



The prostomium is frequently a lobe nearly as wide as 

 the first somite of the body, and sometimes separated from it 

 by a transverse groove; but very frequently grooves extend 

 back into this first somite, one starting from each side of the 

 prostomium, so that the prostomium appears as a narrow or 

 broad lobe embedded in, or '^ dovetailed into," the first somite. 

 Sometimes these lateral grooves stop after traversing the first 

 somite for only a short distance ; the prostomium is then only 

 " partially dovetailed" into the first somite. If, as in Lum- 

 bricus agricola, Hoffmeister, the lateral grooves reach 

 the intersegmental groove dividing the first from the second 

 somite, the prostomium is said to be completely "dovetailed.^' 



The first somite, that surrounding the mouth, is frequently 

 called the '' buccal segment or somite ; " but, following the 

 nomenclature used in works on Polychsetes, I have adopted 

 the word " peristomium " or " peristomial somite" in the 

 following classification. 



Most of the writers of the present day regard this as the 

 first somite, and this is the view I shall take. It may be 

 noted that Vaillant'-^ retains Duges' enumeration, and speaks 

 of the first setigerous somite as the "first" somite. 



In referring to the position of an aperture between two 

 somites I use the form " x/xi/' for example, meaning that such 

 an aperture lies between Somites x and xi. 



' Perrier, " Sur un nouv. Gen. des Lombriciens terrestres," ' Arcb. f. 

 Zool. Exp. et Gen.,' t. ii, 1873. 



' Vaillaiit, " Anueles," ' Suite a Buffon,' 1889. 



