ATOPETHOLID MILLIPEDS — HOFFMAN AND ORCUTT 151 



same species. On the basis of close comparison of this material, we 

 find sufficient differences in body form as well as in gonopod structm-e 

 to warrant recognition of apachellus as a valid form. 



At the present, we consider 8 of the 11 names based on specimens 

 of this genus to be valid, and an additional one is herewith proposed. 

 The locality of the genus appears to be southern Arizona, with a 

 single species known to be from southern California. So far none has 

 been taken in New Mexico or in Arizona north of the Salt River, 

 although this situation may be attributed to the general lack of 

 collecting in the areas mentioned. There is a definite indication that 

 at least several of the named forms are merely allopatric populations 

 of a widespread species, but a satisfactory resolution of their status 

 remains a problem for consideration when ample material has been 

 accumulated for a good revision of the genus. 



The species of Arinolus are among the smallest atopetholids, and 

 are superficially similar under low magnification. In the limited 

 material studied, however, we find that specific differences may be 

 well marked when the animals are closely examined. The characters 

 by which torynophor differs from the other two species treated here 

 are almost generic in nature in comparison with the degree of specific 

 differentiation manifested in other atopetholid groups. 



The anterior gonopods are rather similar in all the kno\vn forms, 

 but the posterior gonopods differ in various small qualitative ways 

 and afford the most tangible recognition characters in the presently 

 very imperfect state of our knowledge of the group. The division 

 between coxite and telopodite is most conspicuous in this genus, there 

 being a flexible joint at the apex of the angle that they form. Distally 

 the telopodite is expanded into a suboval, laminate, somewhat con- 

 choidal development from near the base of which there is a small 

 styliform solenomerito remnant extending medially from one edge of 

 the telopodite. In some forms there is an indication of a groove or 

 duct passing along the base of the telopodite and up onto the base 

 of the solenomerite remnant. This projection is rather clearly homol- 

 ogous with the solenomerite, which is usually quite well developed 

 in the Trigoniulidae. In general, the posterior gonopods of Arinolus 

 are the closest approach to the typical trigoniulid form, and exemplify 

 a primitive condition from which other generic types have evolved 

 by various patterns of simplification or elaboration. The anterior 

 gonopods, however, depart considerabl}^ from the presumably primitive 

 type characteristic of the Eurelinae. 



One name, Arinolus zacatecus Chamberlin (1947b), was proposed 

 for a specimen collected in Zacatecas, Mexico. As is clearly shown 

 by the drawing of the anterior gonopod, this species has the sternite 

 of the Onychehne type, and is obviously not congeneric with A. 



511799—60 5 



