526 OLIGOCHAETA 



(2) Male reproductive apertures closely approximated and placed upon a well- 



marked depression surrounded by a ridge ; penial setae. 



(3) Clitellum, xiii-xix (about). 



(4) Nephridia diffuse. 



(5) Two gizzards generally. 



Tbe genus Trigaster restricted to the West Indies is thus to be defined : — 

 (i) Setae strictly paired. 



(2) Male reproductive openings as in Benhaniia, but no penial setae. 



(3) Clitellum, xiii-xl. 



(4) Nephridia diffuse. 



(5) Three gizzards. 



The New Zealand species, A. Qnultiporus, A. huttoni, A. thomasi, and A. antarc- 

 ticus, may be associated to form the genus Odochaetus which is thus definable : — 



(1) Setae in eight rows, one of two ventral setae of segments xvii, xix 



present. 



(2) Male reproductive openings as in Acanthodrilus ; penial setae present or 



absent. 



(3) Clitellum, xiii-xix. 



(4) Nephridia diffuse. 



(5) Gizzard single. 



Gaeman's (1) genus Diplocardia differs in a good many particulars from other 

 Acanthodrilidae. The most remarkable external variation concerns the position of 

 the spermiducal gland-pores and those of the^ sperm-ducts. These pores are really 

 what they have been sometimes erroneously said to be in other Acanthodrilidae 

 upon segments xviii-xx, instead of upon segments xvii-xix. This fact places the 

 genus in rather an isolated position in the family, unless Peeeier was correct in 

 placing the apertures of the species described by himself in a correspondingly 

 abnormal place. As this difference is enforced by others the genus must, I think, 

 be allowed; the number and position of the spermathecae differs from that found in 

 other Acanthodrilids ; but these organs vary so much in other worms that it seems 

 hardly reasonable to lay much stress on their variation in the case of Diplocardia; 

 there are, contrary to what is found in all other Acanthodrilids, three pairs which 

 are in segments vi-ix. The structure of the spermiducal glands is perhaps, next to 

 the position of the male pore, the chief reason for considering Diplocardia to be a 

 distinct generic type of Acanthodrilid. The single species of the genus — Diplocardia 

 communis — is in some other respects intermediate between Benhamia and Acantho- 



