ATOPETHOLID MILLIPEDS — HOFFMAN AND ORCUTT 149 



The distribution of this subfamily is confined to the Sonoran region 

 of southwestern United States and the Mexican Plateau, centering 

 around Arizona and southern California. Certainly a great number 

 of species remain to be found not only in the areas mentioned but 

 also in the States of New Mexico, Sonora, and Chihuahua, the moun- 

 tains of which have never been explored for their milliped fauna (fig. 9) . 



At present we refer four genera to this subfamily, although with 

 considerable reservation concerning the status of one of them. This 

 matter is discussed at length m connection with the genus Scobinomus, 

 and the diagnostic contrasts made in the second couplet of the fol- 

 lowing key to genera must be considered entirely provisional. 



Key to the genera of the subfamily Arinolinae 



1 Coxites of anterior gonopods produced mesially toward the sternite and 

 separated by two elongate and closely appressed projections of the inter- 

 segmental membrane to form a ligulate process with little or no scleritiza- 

 tion; posterior gonopods short and robust, the coxite and telopodite more or 



less consolidated and immovable 2 



Coxites of anterior gonopods not produced mesially toward the sternite, 

 separated by a broadly triangular projection of sclerotized intersegmental 

 membrane; posterior gonopods long and slender, the coxite and telopodite 

 forming a flexible joint 3 



2. Tergites with rudimentary scobinae and with the caudal margins bisinuate; 



ventrolateral striations of the metazonites produced beyond the edge of the 

 segment into short acute spinules; ends of coUum somewhat obliquely flared 



laterad and readily visible from above Scobinomus Loomis 



Tergites without scobinae and their caudal margins straight; ventrolateral 

 striations of metazonites not produced into distinct spines; ends of coUum 

 not turned outward Tarascolus ChamberUn 



3. Solenomerite of posterior gonopod very long, extending distad well beyond 



the laminate tip of the telopodite; coxal lobes of third leg pair of males 

 elongated, extending back over the coxae of fourth legs: coxal apices of an- 

 terior gonopods only moderately produced distad . . Piedolus Chamberlin 

 Solenomerite of posterior gonopod small and short, less than half as long as 

 conchoidal portion of telopodite; coxal lobes of third legs of males small, not 

 produced distally; coxal apices of anterior gonopods conspicuously produced 

 and elongated Arinokis Chamberlin 



Genus Arinolus Chamberlin 



Arinolus Chamberlin, 1940, p. 81.— Loomis, 1950, p. 164. 



Type species: Arinolus iorynophor Chamberhn, by original 

 designation. 



Diagnosis : Small- to moderate-sized atopetholids with the sixth and 

 seventh segments noticeably enlarged; antennae rather slender and 

 reaching back beyond the collum, the second article equahng or 

 exceeding genal apex; males with tarsal claws of anterior legs of 

 normal size or shghtly enlarged, coxal lobes small and bluntly rounded; 

 sympleurites of seventh segment strongly modified into a rather large 



