62 COOK 



Order Colobognatha. 



The order Colobognatha contains a small series of peculiar Diplo- 

 poda, very different, even in external appearance, from other members 

 of the class. The segments are very short, compact, and numerous. 

 The body is also distinctly flattened, and the projecting sides conceal 

 the legs, so that the Colobognatha are particularly liable to be over- 

 looked as worms, grubs, or slugs. 



Family POLYZONIIDJE. 



There are several tropical families of Colobognatha, but the Poly- 

 zoniidae are a north-temperate group common to both hemispheres. 

 The complete distinctness of the Diplopod faunas of the two sides of 

 North America is strikingly exemplified by the fact that while the 

 Eastern Polyzonium rosalbum is closely similar to the European P. 

 germanicum, there is a new and very distinct genus in the State of 

 Washington to which the attention of collectors in the Northwest 

 should be directed. 



ANALYTICAL KEY TO THE GENERA OF POLYZONIID^E. 



Segments strongly depressed, the dorsum nearly horizontal ; head 



broadly rounded ; segments 20 Genus Platyzonium. 



Segments strongly convex; head conical ; segments 30 to 50. 



Last segment covered and exceeded by the large, broadly rounded, 



penultimate segment; segments 30 Genus Hypozonium. 



Last segment exposed and projecting beyond the distinctly emar- 

 ginate posterior edge of the penultimate ; segments variable in 

 number, adults commonly with 40 to 50 Genus Polyzonium. 



Hypozonium gen. nov. 



The new member of thePolyzoniidse suggests the European Platyzo- 

 nium getschmannii (Zool. Anzeiger, No. 488, p. 426, 1895), rather 

 than Polyzonium. The body is more convex than in Platyzonium, 

 though much less so than in Polyzonium. The body cavity is nearly 

 semicircular in Polyzonium, and about twice as wide as high, but in 

 Hypozonium it is over three times as wide as high, and has the outer 

 corners very narrow. The lateral angles can scarcely be called carinte 

 in the present family, since they are not projections from the sides of 

 cylindrical segments, as in the Merocheta and Coelocheta, but are a 

 direct result of the dorsoventral compression of the body. Among the 

 Merocheta the power of rolling up spirally depends largely upon the 



