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



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

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

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

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

 of the groups of the genital setse. The setse 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 papillse 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 papillse gradually rising until 

 they attain the level of the surrounding integument. Each papilla 

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

 Perionyx gruenewaldi just described ; they are arranged in the same 

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

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

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

 certain amount of ornamentation, which was specially marked in the 

 case of the ventral setse of segment xix. 



In Perionyx macinfoshii 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 Perionyw gigas the cliteilum extends beyond 

 the male apertures. 



In Perionyx intermedins the arrangement is rather different 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 setse of this segment 

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

 observed two setse, 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 setse 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 setse 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 setse near to each male pore, and these pores are 

 placed each upon a separate papilla, both papillse 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 setse of other types — e. g., the genus Mega- 

 scolex ; if the modified setse of Perionyx excavatus were withdrawn 



