150 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lu 



median lobe with a deep notch on either side; anterior gonopods with 

 well developed triangular median projection of the sternite; posterior 

 gonopods distally expanded into a conchoidal or strongly clavate 

 region, with a short slender or spurlike solenomerite remnant. 



Discussion: Although its first species was described by Cook in 

 1911, Arinolus was not recognized as a generic entity until 1940, 

 when Chamberlin named the tj^pe species and diagnosed the genus as 

 follows : 



Differing from Tylobolus and Hiltonius in having a free inner piece to the 

 posterior gonopods as in Spirobolus. The posterior gonopods expanded at distal 

 end into a sj^oonlike lamella. Anterior gonopods with both coxal plate and 

 telopodite extended into processes at mesodistal corners. Anterior sternite 

 proportionately very broad. CoUum acutely narrowed below at each lateral end, 

 margined in front. Claws of two first pairs of legs in the male conspicuously 

 enlarged, those immediatelj^ following more slender and somewhat intermediate 

 in length. Coxae of legs III to VII in the male bearing conspicuous, more or less 

 lamelliform, processes. Anal valves not compressed, somewhat re-entrant at 

 median margin. 



Although this diagnosis is fairly accurate and inclusive, there is 

 some doubt concerning what is implied by the term "free inner piece" 

 of the posterior gonopod. The small spur that occurs on the telopo- 

 dite in Arinolus is clearly not homologous %vith the long processes 

 that originate from the base of the telopodite in species of the 

 Spirobolidae. In general, the diagnosis of Arinolus would have been 

 much more improved and manifestly much more meaningful had com- 

 parison been made with other atopetholids (particularly Piedolus) 

 rather than with genera belongmg to a different suborder. 



Subsequent papers by Chamberlin (1940, 1941a, and 1947b) included 

 the descriptions of several new species, so that the genus contained 

 six nominal species by 1950. In that year appeared the first and 

 only published discussion of taxonomy m the group, by H. F. Loomis, 

 in which he dealt with the 1911 Onychelus species of Cook, and sug- 

 gested the synonymy of several Chamberlin names. His proposals 

 may be summarized as follows: Arinolus apachellus Chamberlin 

 (1941a) = A. torynophor Chamberlin (1940) ; Arinolus hopinus Cham- 

 berlin (1941a) == Onychelus hospes Cook (1911); Onychelus suturatus 

 Cook (1911) = 0. dentatus Cook (1911). 



The last two are in all probability correctly evaluated since the 

 type localities of the species involved are the same, and since the 

 forms of Arinolus are largely allopatric. There is, however, reason 

 to challenge the synonjnny of A. apachellus under A. torynophor, an 

 association made chiefly on the basis of gonopod similarity. Loomis 

 has kindly loaned the material upon which his opinion was based, 

 a male topotype of torynophor and several specimens from the San 

 Tan Mountains near Sacaton, Arizona, that he took to represent the 



