DESCRIPTIOiMS OF GENERA AND SPECIES 365 



from most other worms which have been called 'Perichaeta,' except those that 

 have just been referred to. It might be supposed that the differently arranged 

 nephridia were present in addition to the paired tubes, as in Megascolex armatus. 

 In P. intermedia this diffuse network is certainly not present, nor in P. dendyi, &c. ; 

 the excretory system is represented by the paired tubes and nothing else. The tubular 

 atria occur in P. bakeri, of which Fletcher says (4, p. 6i8): 'The two prostates 

 occupy xviii and xix, each of them being a long narrow body coiled into a compact 

 mass, the duct coming off from the anterior portion of the gland ^.' It does not appear 

 clear whether P. barronensis has the same kind of ' prostate ' ; this is what Fletcher 

 (2, p. 961) writes on the matter: 'In xiii a pair of prostates, their proximal portions 

 long, narrow, continuous with the genital ducts, looking more like convoluted thick- 

 walled tubes than solid glands, their distal portions a little more compact;' at 

 any rate, P. dendyi and several of Spencer's species have. I have proposed to 

 separate P. intermedia as a distinct genus of Perichaetidae, characterised by the two 

 points mentioned above. On studying the worm afresh for the purposes of the present 

 work, and in the light of Benham's paper upon the curious Acanthodrilid genus 

 Plagiochaeta, I am not convinced that P. intermedia might not perhaps be referred to 

 the Acanthodrilidae ; the smooth appearance of the worm is much more suggestive of 

 an Acanthodrilid than a Perichaetid, and such trifles often are indications of affinity. 

 Unfortunately, I am unable to report upon the relation of the sperm-duct to the 

 distal glands, a point of great importance in the discrimination of such affinities 

 as those treated of here. I should include in this genus a number of the Australian 

 species duly enumerated below. 



MiCHABLSEN has proposed to separate under the name of Pleionogaster 'those 

 Perichaetidae, which have several gizzards behind the clitellum in addition to the one 

 in front.' The two species which refer to this genus, viz. P. Jagori and P. samariensis, 

 agree with my P. horsti, described some years previously (41), in the following 

 characters besides that mentioned by Michaelsen : — 



The setae are very numerous in some of the segments; there are as many as 

 150 on the sixth segment of Pleionogaster horsti. As in the genus Megascolex there 

 are no caeca, and the clitellum is composed of four segments ; the anterior gizzard too 

 is peculiar in occupying a single segment only, the eighth. The setae as in Perichaeta, 

 have no dorsal and ventral gaps ; the characters of these species are, in fact, intermediate 

 between those of Megascolex and Perichaeta, with the addition of a few characters 

 peculiar to the species, and not found either in Perichaeta or in Megascolex. 



' But the description of an ' U-shaped ' duct is not, perhaps, in accord with the suggestion that P. bakeri 

 has tubular atria. 



