igil] NORDAMERIKANISCHE HyDRACHNIDEN. 293 



finely pectinate on both sides; on the inner side, dose to the latter is 

 a somewhat longer, likewise pectinate bristle. On the inner side of the 

 third segment are six peculiarly arranged and very long bristles; these 

 are densely or loosely pectinate, some on one side, some on both sides 

 (Fig. 18). On the flexor side of the penultimate segment, near the middle, 

 is a short, projecting, strongly-bent bristle. 



The epimeral region, which is 747/^ in length, apparently does not 

 project beyond the frontal margin of the body and covers not quite 

 two-thirds of the ventral surface; laterally it fails to reach the body- 

 margin; its greatest breadth is 664/ti. The genital emargination is l66At 

 long and is a trifle longer than the maxillary emargination (150/i). The 

 common posterior end of the second pair of plates has a very slight breadth 

 (33^)- The median suture of. these epimera is longer than half the dis- 

 tance between the maxillary and genital emarginations. The suture 

 between the third and fourth plates extends distinctly as far as the genital 

 emargination. The last epimeron is of little breadth and terminates be- 

 hind in a regular curve. The position of the basal articulation of the hind 

 legs is in the middle between the suture mentioned and the posterior 

 margin of the last epimeron (Fig. 19). At the end of the epimeral pro- 

 cess beside the maxillary emargination is a membranous appendage, 

 which apparently represents the base of attachment of a bristle. The 

 lengths of the legs measured from first to last are: 713, 913, 913 and 12^5/1. 

 The segments are all rather stout, recalling, on the whole, the legs of 

 Thyas; towards the distal end they taper but little; the tarsus of the 

 third last pair of legs is slightly thickened and its ungues enlarged ; its 

 length is 45-65/*; the basal part of the same segment has but a slight 

 breadth (10-15/1) and thus, as in L. angulata Sig. Thor., has no leaf-like 

 expansion. The leg bristles resemble those of the species of Thyas, in 

 consisting chiefly of stout spines ; they occur most abundantly on the ex- 

 tensor side of the middle segments of the legs and in circles at the ends of 

 the segments. Except a few very short and fine hairs scattered here and 

 there, swimming hairs are entirely wanting. 



The genitalia, measured from the valves, are i66/i long and 149/Lt 

 broad posteriorly; they extend beyond the epimeral emargination to a 

 distance of about one-third of their length. The inner margin of each 

 valve is densely clothed with hairs; the anterior hairs are short, posteriorly 

 they become gradually longer. The most anterior acetabulum has an 

 elongate-elliptical form, the two succeeding ones are roundish (Fig. 19). 

 The sex of the specimen here described was not recognized. 



The anal opening is situated about the middle between the genitalia 

 and the hind margin of the body. 



