21 



9. Cymbasoma rigidum, Thompson. 



(PI. X, fig. 2, PI. XI). 



rigida, J. C. Thompson, Linn- Soc. Jouru. /.oo!., Vol., XX, p. l.'il, PI. 



XIII, figs. 1-4. 



Syn : Monstrilla rigida, Bourne 1 . 

 Thainnalens rigidus, Scott. 

 Thanrnalens Clapnredi. Giesbrecht. 

 Tfuuinialens gertnanicus, Tim in. 

 . Htrmocera Dance, Malaquin. 



Specific Characters. Female. Body moderately slender, and generally 

 extended in a manner to give it a somewhat rigid appearance. Cephalic seg- 

 ment fully as long as the remaining part of the body and, viewed dorsally, 

 somewhat dilated in the middle, ventral face evenly convex throughout. Tail 

 scarcely exceeding half the length of the exposed part of the trunk; genital 

 segment of moderate size and evenly narrowed behind, ovigerous spines nearly 

 3 times as long as the tail; distal segment somewhat flattened and gradually 

 widening behind, exhibiting in front of the middle, on each side, a slight 

 notch, as an attempt to a subdivision, the notch not being, however, continued 

 in any difining suture. Caudal rami only slightly longer than they are broad, and 

 not much divergent, with the inner edge somewhat concaved, the outer gib- 

 bously produced, each ramus provided with 3 strong subequal setae, the outer- 

 most of which is attached to a rather prominent ledge; a very small appendi- 

 cular bristle is moreover generally found attached near the inner corner to the 

 ventral face. Eye well developed, with all 3 lenses distinct. Antennas rather 

 short, scarcely attaining l /a of the length of the cephalic segment, terminal 

 joint somewhat shorter than the other 3 combined, with none of the setae 

 ramified. Oral tubule rather small, and occurring at about the end of the 

 first 1 U of the cephalic segment. Natatory legs with the outher ramus only 

 slightly longer than the inner, its terminal joint not much produced. Last 

 pair of legs with 3 apical setae, the innermost of which is much smaller than 

 the other 2, inner edge produced to a narrow linguiform lobe curving outwards 

 along the terminal part of the leg, and in most cases extending as far as the 

 latter. Ova attached to the genital filaments very numerous and in some 

 cases accumulated to form an elongate almost cylindrical mass extending far 

 beyond the limits of the body. 



Male, as usual, smaller than female and of a shorter and more robust 

 form of the body, with the cephalic segment somewhat clavate in outline. 

 Tail rather narrow and composed of 3 segments, the last exhibiting on each 



