414 The American Naturalist, 



[May, 



has proved necessary to establish genera and families in attempting to 



properly recognize their structural novelty and diversity. Some of 

 these new groups have already received names, 2 but their characters 

 have been only formally indicated. 



Family Ammodesmidje. 

 Two minute Glomeroid genera were discovered, one of which, Am- 

 modesmus, is the smallest member of the suberder, if not of the entire 

 class. The only species, Ammodesmus granum, is less than two milli- 

 metres long, and about half a millimetre broad. A single specimen 

 was secured while collecting minute Oniscidse, but diligent and repeated 

 search failed to find another. It did result, however, in three spec- 

 imens of a very distinct, though evidently allied, genus which it is pro- 

 posed to name Cenchrodesmus. Both genera have the habit of coiling 

 into a sphere. The second segment is enormously enlarged so as to 

 completely conceal the head and first segment when viewed from the 

 side, as well as to cover the space left between the decurved carinse of 

 the other segments when the creatures are coiled. Ammodesmus has 

 the dorsum roughened by a transverse row of large papilliform tuber- 

 cles rising from the posterior part of each segment, while Cenchrodes- 

 mus volutus has the segments nearly smooth. The surface of Ammo- 

 desmus is rough and dusted with earth. When disturbed it coils up 

 and lies motionless, and is then perfectly concealed, having exactly the 

 appearance of a grain of sand. My specimen would certainly not have 

 been seen had it not been crawling. Cenchrodesmus is pinkish in life 

 and mottled with pale horn-color in alcohol. Both genera live on the 

 ground under decaying wood or leaves. 



Family Campodesmid^e. 



This also contains two genera similar in size and general shape, yet 

 evidently distinct, in that Campodesmus has the segments ornamented 

 with two conspicuous clusters of coarse tubercles, while Tropidesmus 

 jugosus has two transverse rows of short longitudinal carinse, a form of 

 sculpture previously quite unknown in Polydesmoidea. The carina? 

 are depressed in both genera, and the dorsal surface is very rough with 

 fine granules and tubercles. Pores are visible on the fifth and seventh 

 segments, but I have been unable to find them on the others. Both 

 forms are denizens of the deepest forests, where the light is so deficient 

 that they are sure to be overlooked unless specially sought for. They 

 are very sluggish in their movements, and are seldom found crawling. 

 When disturbed they coil up into a spiral, and also assume that posi- 



J Proc. U. S. Nat. Museum and Annals N. Y. Acad. Science, 1895. 



