118 PROCEEDINGS OF THE NATIONAL MUSEUM TOi-. 8* 



Male genitalia iii two distinct parts; the anterior part of two 

 erect, thin, convex, subtriangular pieces, in contact mesially from the 

 broad base to the acute tips ; posterior gonopods erect, subcyhndric, 

 but each with a channel extending inward and upward from the 

 outer side of the base to the apex ; the apex strongly expanded and 

 with an outwardly produced, bifurcate arm arising from the con- 

 cave face of the inner lobe; under high magnification the lower 

 branch of the bifurcate arm is seen to be equipped with several tiny 

 appressed barbs. The large anterior and posterior pieces at the 

 base of the gonopods in Diactis have no recognizable counterparts 

 in this genus. 



The ovipositors of tlie female, when extruded, are seen to consist 

 of two long, indistinctly jointed appendages, with the last joint 

 especially long and very strong clavate, thickest near the apex ; the 

 distal half of the joint with a broad, longitudinal section along the 

 outer side gradually raised distad, the end rapidly constricted to a 

 narrowly rounded apex which scarcely exceeds the inner, swollen 

 portion of the joint; basal half of the joint glabrous, the apical half 

 with moderately long, erect bristles, which are less numerous on the 

 lateral elevation except at its tip. 



Males with a comb of hairs on the under side of the last joint of 

 legs 1 and 2 ; a velutinous pad occupying the under side of the last 

 joint of legs 3 to 7, and usually several pairs following the gonopods, 

 where the pads gradually decrease in size. Coxae of the seventh legs 

 and of the legs near the middle of the body without special lobes 

 such as are present on these legs in Diactis. 



Females with a comb of hairs on the first two pairs of legs as in 

 the male but without velutinous pads on any of the ensuing legs. 



TYNOMMA SEDECIMUM, new species 

 FiGUBES 17, j-l; Plate 3, Figuke 6 



Description. — Body 15 to 18 mm long and 1 to 1.2 mm wide; with 

 46 to 52 segments. 



Eye cluster very small, composed of only 22 to 28 ocelli in 6 or 7 

 rows ; sense organ considerably larger than an ocellus and located in 

 front of rows 4 and 5, or rows 5 and 6 of the cluster. 



First segment with only 16 crests; excepting the uniformly large 

 lateral crests the others alternate in size like the crests on the second 

 segment, although there are no secondary crests between the inner 

 pair of prmiary crests ; median crests extending across the basal two- 

 fifths of the segment, the two outer crests on each side nearly twice 

 as long as the median crests. 



Segments 2, 3, and 4 with the inner pair of primary crests almost 

 parallel, very slightly spread apart behind. 



