142 PHILORTHRAGORISCUS SERRATUS. 



the external distal angle. In the inner branch the lateral 

 margin of this joint is fringed with hairs. The terminal 

 joint of the inner branch bears on the distal half of 

 its margin seven plumose setae, whereas the proximal 

 half is provided with hairs. In the outer branch the ter- 

 minal joint shows externally a row of eight small conical 

 tubercles, followed by four spines and more internally by 

 five plumose setae. 



The third pair of swimming feet (fig. 8) is especially 

 characterized by having the inner part of its basal joint 

 produced in a large elliptical swimming plate, equalling 

 in largeness the unpaired abdominal plate. The branches 

 of these feet resemble generally those of the second pair, 

 they are only more faintly developed. The terminal joint 

 of the inner branch bears but four instead of seven plu- 

 mose setae, that of the outer branch instead of five only 

 four. The proximal joint of the outer branch is asymme- 

 trical , by having its external half produced in a rounded 

 plate, ending in a spine. In Dinematura this pair of feet 

 has a quite different appearance and both branches are 

 three-jointed. 



The fourth pair of swimming feet (fig. 10) is rather small 

 and totally covered by the preceding pair ; it consists of 

 an almost circle-round basal joint and two branches, each 

 formed by a single joint of which the inner measures 

 only a third of the length of the outer one. This latter 

 bears at the outer side two, at the inner side three spines 

 and is armed at the end with a long and a short spine; 

 the shorter inner branch has only three small spines at the 

 extremity. The basal joint is externally from the base of 

 the outer branch provided with a seta. It is especially the 

 rudimentary character of the last pair of feet, that makes 

 me hesitating to refer this species to the genus Dinematura', 

 in this genus the branches of the fourth pair of feet, though 

 also single-jointed and without plumose setae, are produced 

 in large plates, extending beyond the third pair of feet, 

 and their basal joint is provided with winglike processes. 



Notes from the Leyden IMuseuni , Vol. XIX. 



