78 



Fam. 9. Idyidae. 



Characters. Body more or less depressed, with the posterior division be- 

 coming abruptly much narrower than the anterior, both with the normal number of 

 segments. Eye distinct or wanting. Anterior antennae more or less slender, 8- or 

 9-articulate, distinctly prehensile in male. Posterior antennae 3-articulate, with 

 the outer ramus well developed. Oral parts differing somewhat in structure in 

 the different genera. First pair of legs, as a rule, with both rami 3-articulate, 

 but of rather different structure, the inner one generally the longer and always 

 prehensile. Natatory legs normal. Last pair of legs more or less extended 

 laterally, proximal joint but slightly expanded, distal joint more or less elongated. 

 A single ovisac present in female. 



Remarks. The forms belonging to this family are chiefly characterised 

 by the sharp demarcation between the anterior and posterior divisions of the 

 body, the former being more or less expanded and depressed, the latter abruptly 

 much narrower. In the structure of the several appendages, some approach may 

 be found, partly to that in the PorceUidiidcK, partly to that in the Thalestridcs. 

 The shape of the last pair of legs is, however, rather different from that in either 

 of those 2 families, and agrees more with that found in the Pcltidiidce. We 

 know as yet of 6 different genera belonging to this family, all of which are re- 

 presented in the fauna of Norway. 



Gen. 21. ASpldiSCUS, Norman, 1868. 



Syn: Scutellidium, Brady (not Glaus). 



Generic Characters. Anterior division of body much expanded and de- 

 pressed, clypeiform, with the dorsal face slightly vaulted and very smooth. Ce- 

 phalic segment large and evenly curved in front, and, like the epimeral plates, 

 bordered by a narrow hyaline rim; rostrum lamellar, distinctly denned at the 

 base. Epimeral plates of the first 3 free segments of metasome well developed, 

 imbricate, recurved; 3rd segment fornicate behind, arching over the very small 

 last segment, as also over the anterior part of the urosome. The latter abruptly 

 much narrower than the anterior division and gradually tapering distally, genital 

 segment scarcely expanded. Caudal rami very small, but with the apical setae 

 much elongated and extending straight backwards. Eye distinct, of usual 



