Occasional Papers of the Museum of Zoology 75 



CRYPTODKSMIDAr: 



Arionus, gen. nov. 



Body composed of head and twenty segments. 



CoUum covering the head ; its anterior border divided into 

 ten areas by radial lines as in Docodesmus, etc., elsewhere 

 granular. ' 



Second tergite broader than coUuni and than third tergite, 

 its lateral border showing these areas separated by short radial 

 lines. Other tergites with keels comparatively narrow; pre- 

 senting three lateral areas separated by impressed radial lines 

 and slight marginal indentations, or occasionally on one or 

 both sides, in more posterior segments four lobes. Caudal 

 margin of keels with one incision. Keels continuing nearly 

 the general outline of dorsum. Caudal border of metatergites 

 divided into a series of areas by longitudinal impressions, the 

 margin correspondingly weakly crenate. Pores inconspicuous, 

 on caudal lobe back from margin; occurring on segments live, 

 seven, nine, ten, twelve, thirteen, fifteen to [nineteen. Dorsal 

 surface of metatergites coarsely granular or tubercular, tuber- 

 cles nearly uniform. 



Penult tergite with caudal margin convex, the areas, of 

 which there are six in all in the genotype, produced caudad as 

 stout acute teeth, of which the lateral one on each side or 

 process of keel is not larger than others, which accordingly 

 extend farther caudad. 



Anal tergite^ small, now lobatc, with cauda exposed from 

 above. 



Gonopods of male with coxae large. The telopodite also 

 large and stout, exposed in lateral view. 

 Genotype, A. ulopJiihts. sp. nov. 



