232 W. B. BENHAM. 



The dorsal vessel is double throughout its lengthy and is 

 enclosed in a special coelomic tube.] 



Species 1. D. benliami, F. E. B. ; New Zealand. 

 See Beddard, ' Quart. Journ. Micr. Sci./ xxix. 



Doubtful Genus. 



Neodrilus monocystis, F. E. B., New Zealand. 

 Founded on a single specimen, and differs from Acantho- 

 drilus in possessing a single pair of prostates and a single 

 pair of spermathecae. It appears to me very doubtful whether 

 this should be considered as a new genus, or whether the 

 characters are merely some peculiar variations of A cant ho - 

 drilus. 



Remarks on the Acanthodrilidae. 



The genus was originally characterised by the presence 

 of two pairs of male pores ; it is only recently that Beddard 

 has shown that these pores belong to the prostates, and that the 

 sperm-ducts open by a pair of pores on the eighteenth somite. 

 The chief points of difference between Acanthodrilus and 

 Trigaster lie in the fact that the male pores and atriopores 

 in the latter genus are in a pit (in my original description I 

 placed the atriopores in xvi, xviii ; I believe that this statement 

 is wrong, and that the prostate-pores and spermiducal pores are 

 placed as in Acanthodrilus), and in the absence of penial or 

 copulatory setae and the presence of three gizzards. When the 

 genus was formed, the only worm with more than one gizzard 

 (except Moniligaster) was Digaster. That the existence 

 of three gizzards is not generic is now established by the 

 formation of Michaelsen of a species, T. rosea, with only 

 two gizzards. 



Three species of Acanthodrilus are known with two 

 gizzards — A. buttikoferi and A. beddardi of Horst; 

 and A. scioanus, Rosa. 



Horst also figures the prostate-pores in A. schlegelii as 

 situated in a fossa. 



But the great extent of the clitellum in Trigaster, to- 



