688 MR. F. E. BEDDARD ON NEW [DcC. 20, 



close together, are really ia a line which is in the same direction as 

 the circle of setae of the segment ; there is, however, a gap between 

 the last seta of the ring of unmodified setae and the first of the 

 genital setae. The atrial pores are just in front and to the outside 

 of tlie groups of the genital setae. The setae themselves have been 

 figured by Michaelsen. 



In Perionyx excavatus the male genital apertures are each 

 placed upon a semicircular elevation, the two being in close contact. 

 These flat papillae are both depressed below the surface of the 

 surrounding integument ; this depressed area appears to be only 

 sharply marked off anteriorly and posteriorly by grooves ; laterally 

 there is no sharp demarcation, the papillae gradually rising until 

 they attain the level of the surrounding integument. Each papilla 

 has 5 or 6 genital setae of a precisely similar appearance to those of 

 Perionyx p-uenewaklijust described ; they are arranged in the same 

 way, being continuous with the line of setae of the segment and 

 are separated from them by a space. These genital setae are also 

 longer than the ordinary setae of the body, but the latter show a 

 certain amount of ornamentation, which was specially marked in the 

 case of the ventral setae of segment xix. 



In Perionycc macintoshii the ventral area which bears the atrial pores 

 forms a sucker-like structure completely sunk below the level of the 

 surrounding epidermis ; it measured in one individual 3 mm, across. 

 This difference from the other two species may possibly be correlated 

 with the fact that in Perionyx gigas the clitelkmi extends beyond 

 the male apertures. 



In Perionyx intermedius the arrangement is rather difierent from 

 that which obtains in the two species just described. The xviiith 

 segment is widened in the middle ventral line ; the integument 

 has a tumid swollen appearance, and there is a transverse groove 

 into which open the atrial pores. The row of setae of this segment 

 are not continued over the median area, but in one specimen I 

 observed two setae, one on each side at the bottom of the groove 

 already referred to. As the extremities of these were unfortunately 

 broken off I am not able to say whether they showed any more 

 marked ornamentation than the other setae of the body ; in any 

 case they were not different in form. 



It will be seen from the above details that the genus, as we at 

 present know it, falls into two subdivisions. In Perionyx macin- 

 toshii and P. intermedius there are no specially modified setae in the 

 neighbourhood of the male pores, and the latter are placed upon a 

 median area which is not divided by a cross furrow into two areas, 

 one for each pore. 



In Perionyx excavatus and P. gruenewaldi there is a group of 

 specially modified setae near to each male pore, and these pores are 

 placed each upon a separate papilla, both papillae being enclosed 

 within an area marked off from the surrounding integument. 



It appears to me that in this genus we have an early stage in the 

 evolution of the penial setae of other types — e. g., the genus Mega- 

 scolex ; if the modified setae of Perionyx excavatus were withdrawn 



