516 OLIGOCHAETA 



opens on to a penis, and which also receives sperm-ducts. On segment in front 

 (XVII) open anterior pair of spermiducal glands. 



Nannodrilus africanus, BEDDARD. 

 N. africanus, BEDDARD, P. Z. S., 1894, p. 388. 



Definition. Length, about 2 in. Clitellum, XIII-XVII. Septa, V/IX, thickened. Rudi- 

 mentary gizzards in VII, VIII. Nephridia commence in V, without end sac. Last 

 heart in XI. Spcrmathecae, one pair in VII, without diverticulum. Hal. West 

 Africa ; aquatic. 



FAMILY ACANTHODRILIDAE 



DEFINITION. Large or small Oligochaeta, usually terrestrial, occasionally aquatic, in 

 habit. Setae, 8, 12, or numerous upon each segment of the body. Male pore 

 upon segment XVIII ; pores of spermiducal glands upon segments XVII and 

 XIX 1 . The latter are tubular structures, generally accompanied by penial setae. 

 Spermathecae, nearly always two pairs in segments VIII and IX with 

 diverticulum or diverticula. 



Anatomical characters. 



The Acanthodrilidae are of various sizes ; they range from 29 mm. to several 

 feet in length. They have all of them a prostomium, which may be either simply 

 a prolongation of the buccal segment, or may be received into an excavation of 

 the anterior margin, or may be, in addition, continued on to the buccal segment by 

 grooves which are in many cases (e. g. Acanthodrilus novae-zelandiae) prolonged as far 

 as the posterior limits of that segment. 



The setae are never ornamented at the extremity 2 , as in the Geoscolicidae ; they 

 are usually eight in each segment ; but in Deinodrilus there are twelve to each 

 segment, and in the genus Plagiochaeta 25-27 couples of setae. When the number 

 of setae is restricted to eight, these may be arranged in closely approximated couples 

 (e. g. A. unyulatua), or may be somewhat separated from each other, as in Octochaetus 



' Diplomrdia is the only certain exception to this statement. 

 3 Except in the case of Bmhamia togoensis. 



