248 W. B. BENHAM. 



See Perrier, ' Nouv. Arcli. du Mus. d^Hist. Nat. de Paris, 

 viii, 1872; Beddard, 'Ann. Mag. Nat. Hist./ 5th Series, 

 vol. xii, 1883; 'Proc. Zool. Soc./ 188G ; Bourne, ' Proc. Zool. 

 Soc.,' 1886; Rosa, 'Ann. d. Mus. Civico d. Storia Nat. d. 

 Genova,' vi, 1888. 



Remarks on Perionycidae. 



In external characters Perionyx agrees exceedingly closely 

 with Perichseta. In the former, however, the male pores are 

 close together in a median pit, whereas in most species of 

 Perichseta they are rather wide apart, and on papillae. 

 Again, the clitellum does not so completely obliterate the 

 segments and the grooves in Perionyx (nor are its limits so 

 distinctly defined) as in Perichseta. The absence of caeca, 

 and of any other diverticula of the alimentary canal, and the 

 presence of large nephridia, are characters said to be found in 

 some species of Perichseta. The median position of the ovi- 

 ducal pore has certainly a striking resemblance to that of 

 Perichaeta. It may be possible to transfer those worms with 

 large nephridia, with forward position of the gizzard, without 

 caeca, and with closely approximated male pores, which are at 

 present regarded as species of Perichaeta, to the genus 

 Perionyx. 



At present only three species have been described: P. ex- 

 cavatus, E. P.; P. Mclutoshii, F. E. B.; and P. saltans, 

 A. G. B. — the last two very briefly. 



B. There is no hollow prostate in connection with or in 

 the region of the male pore. 



1. The male apertures are behind Somite xvm, within the 

 area occupied by the clitellum. 



a. Eight setae, separate or even alternate in some part of 

 the body. There is only one pair of sperm-sacs, which 

 extend through several somites. 



