GENUS NOTHHUS. 485 



a rounded cliitinous elevation in the upper median line, 

 near the distal end, bearing setiform hairs (PI. XL VII, 

 fig. 10). The claws are generally tridactyle, sometimes 

 with the central unguis smaller than the others ; but 

 some species are monodactyle. The legs in most 

 species are bordered by thick curved spines, which 

 even are present on the tarsi. 



The Abdomen is almost always flat, generally level 

 or hollow on the notogaster, although there may be 

 elevations and depressions. N. theleproctiis appears 

 less flat than other species, but this is partly in conse- 

 quence of the mode of carrying the cast skins. The 

 outline of the abdomen is generally more or less 

 oblong {N. horridus, &c.), or else shield-shaped (N. 

 tardus, &c ) ; its hind margin is apt to be provided 

 with chitinous apophyses and other projections (PL 

 XL VIII, fig. 7) which bear large spines or hairs. 

 Similar structures are often found a little within the 

 lateral and anterior margins, but they are usually 

 small, although they attain a large size in N. spiniger. 

 The lateral margins of the abdomen are generally 

 raised. 



The Genital and Anal Plates are always large, and 

 generally close together ; the former are usually pen- 

 tagonal and the latter often come to a point posteriorly 

 (PI. XLVII, fig. 2). 



The Ventral Plate is sometimes reduced to a mere 

 strip ; this is partly in consequence of the dorsal plate 

 being much reflexed, or rather sufflexed, on to the 

 ventral surface, and partly in consequence of the large 

 size of the genital and anal plates and their proximity, 

 so that but little space is left between them and the 

 dorsal plate ; but if some of these species, e. g. N. 

 homdus, be dissected, it will be found that, in conse- 

 quence of the imperfect chitinization of these parts, 

 and the thickness of the membrane joining them, the 

 ventral plate is far less distinct from the genital and 

 anal than is the case in most genera. 



The Tracheae in such species as I have examined, 



