462 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 85 



These markings are not in contact and usually are so placed as 

 to form four corners of a square, with two of the markings presetal 

 and two postsetal. This arrangement is, apparently, quite char- 

 acteristic, as the only variation on any of the seven worms is the 

 absence of the median presetal marking of one or both sides. Tlie 

 male setae of xviii are continued onto the porophore nearly to the 

 male pore area, but on the ventral face of the porophore they are 

 smaller and more closely crowded than midventrally. The setae 

 in the region between the two pairs of genital markings, on some 

 specimens, are so closely crowded as to be forced anteriorly or 

 posteriorly out of line in such a way as to produce a zigzag appear- 

 ance. A similar zigzagging of a setal row is apparent on two speci- 

 mens, on xvii on each side just anterior to the male porophore. 



The male porophores certainly represent an everted condition of 

 some sort of a male pore invagination. In a carefully dissected 

 specimen the porophore can be retracted at least pai'tially. If, in 

 a completely retracted condition, there is a true copulatory cham- 

 ber, then the four genital markings and the small closely crowded 

 setae will probably be withdrawn into the interior of the chamber. 

 A lateral lip similar to that which can be seen on those specimens 

 with slightly retracted male pore areas is, however, usually asso- 

 ciated with a deep parietal invagination, which does not reach 

 through the body wall into the coelomic cavity. If the male pore 

 invagination in P. pectenifera is a parietal invagination of this sort, 

 then in a retracted condition the four genital markings and the 

 small closely crowded setae may be invisible from the exterior. 



Aside from the markings on the ventral face of the male porophore 

 there are no postclitellar genital markings. The preclitellar genital 

 markings are of two sizes. The smaller markings are on the poste- 

 riormost margins of vi-viii in close proximity to the spermathecal 

 pores. There are usually three of these markings, one immediately 

 anterior to, one immediately lateral to, and one inunediately median 

 to each spermathecal pore, but both the lateral and median mark- 

 ings may be lacking or only the anterior marking. These markings 

 and the spot on which the spermathecal pore is located are of a 

 grayish trans! ucence and so closely crowded together that identifi- 

 cation of the spermathecal pore and of the margins of the markings 

 is difficult. 



The larger, paired markings are presetal on vii, viii, and ix and 

 postsetal on vii and viii; each marking in 5-8 intersetal intervals 

 median to the spermathecal pore and usually slightly nearer to the 

 setae than to the intersegmental furrow. One marking of a pair 

 may be lacking, or an additional marking may be present close to 

 one of the usual markings. The presetal markings of ix are lacking 



