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Show 688 MR. F. E. BEDDARD ON N E W [Dec. 20, close together, are really in a line which is in the same direction 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 the 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 gruenewaldi just 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 Perionyx 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 m m . across. This difference from the other two species may possibly be correlated with the fact that in Perionyx gigas the clitellum extends beyond the male apertures. In Perionyx intermedius 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 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 macintoshii 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 Megascolex ; if tbe modified setae of Perionyx excavatus were withdrawn |