GENUS NOTIIKUS. 481 



natus, and JV^. invenustus, these creatures are very 

 similar, aud their parts, even to the hairs, are homo- 

 logous, so that at first I was inclined to think that 

 they might be all varieties of one species. I was, 

 however, forced to abandon this idea because, on 

 gathering a long series, it was evident that there were 

 a number of small characteristics, each trifling in itself, 

 but which broke up the series into perfectly constant 

 groups ; the four or five constituting, say, group A not 

 being in any way connected by features, but being 

 invariably found together; and none of them ever 

 being found supplied with the characters included in 

 groups B, C, or D. When once these small differences 

 have been ascertained it is not difficult to identify the 

 species, provided you can get the specimens clean 

 enough to enable you to see them. 



The genus is one in which the cuticle of the abdo- 

 men in most of the adults is not so hard nor so 

 thoroughly chitinized as in other groups, consequently 

 the creatures protect themselves either by carrying 

 the cast notogastral skins, as N. theleproctus, or more 

 frequently by piling dirt and debris upon their backs. 

 This extraneous material appears to be attached by 

 some glutinous secretion, which renders the process 

 of cleaning very difficult unless such chemicals as 

 sodium-hydrate be employed. The dirt adhering to 

 the back doubtless also serves for concealment. They 

 live very much at the roots of mosses, &c., and when 

 one or two N. horridus or N. hiverrucatus are placed in 

 a cell with a little of the earth they were taken from 

 it is extremely difficult to find them, even if the 

 searcher has placed them there himself and knows 

 that they must be there. 



The Rostrum, is generally short, sometimes slightly 

 trifid {N. theleproctus, PI. XLV, fig. 1, &c.), some- 

 times slightly truncated {N. Tcwgionii, N. horridus, 

 &c.). In the horridus group and some other species 

 the rostrum is a very small, narrow, truncated cone, 

 the cephalothorax widening suddenly behind it. The 



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