516 OLIGOCHAETA 



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

 (XVIl) open anterior pair of spermiducal glands. 



Nannodrilus afrieanus, Beddaed. 



K". afrieanus, Beddaed, P. Z. S., 1894, p. 388. 



Definition. Length, about % in. Glitellum, XIII-XVII. Se^ta, V/IX, thickened. Rvdi- 

 mentary gizzards in VII, VIII. Nephridia commence in V, withont end sac. Last 

 heart in XI. Sjaormathecae, one pair in VII, without diverticulum. Hah. — West 

 Africa ; aquatic. 



Family ACANTHODRILIDAE 



Depinitiom'. 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 ^. 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 prostomiuvi, 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-zelaTidiae) prolonged as far 



as the posterior limits of that segment. 



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



are usually eight in each segment ; but in Beinodril/ws 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. ungulatus), or may be somewhat separated from each other, as in Octochaetus 



^ Biplocardia is the only certain exception to this statement. 

 " Except in the case of Benhamia togomsis. 



