260 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



Phylogenetic Relationships 



To the best of my knowledge no one has yet expressed an opinion 

 concerning the systematic position of Cherokia or its relationships 

 to other genera, aside from a remark in my 1950 treatment that: 

 "The disparity in sizes of the [cyphopod] valves suggests relation- 

 ships with Zinaria, as does the nature of the sternites and male 

 gonopods." Since then I have found no reason to revise this state- 

 ment, but have come to recognize other genera as perhaps even more 

 closely related to Cherokia. These form a discrete natural group 

 worthy of formal tribal recognition: 



Rhysodesniini, new tribe 



I propose this tribe for xystodesmid genera hi which the coxae of 

 the gonopods are attached to a distinct slender sternite and join the 

 prefemora at a right angle and in which the postcoxal division of the 

 telopodite is typically nearly straight and the prefemur elongate and 

 not globosely enlarged basally. When present, the prefemoral process 

 is simple, slender, and acicular. These genera include polymorphic 

 species of very variable form, in which the general form of the male 

 gonopod is subject to little, if any, specific modifications. 



The following genera (the validity of some of which seems not to be 

 beyond challenge) at present constitute the tribe: 



Rhysodesmus Cook, 1895 Howellaria Hoffman, 1950 



Cruzodesmus Chamberlin, 1943 Cherokia Chamberlin, 1949 



Acenlronus Chamberlin, 1943 Pleuroloma Rafinesque, 1820 2 

 Boraria Chamberlin, 1943 



The first five names of the list represent closely allied species groups, 

 which some authors might prefer to unite in a single genus. The last 

 two are much more strongly differentiated, to the extent that probably 

 no one would question their claim to generic rank. Rhysodesmus, in 

 particular, is highly variable and about 80 species have so far been 

 described. The others are less extensive, and their rate of evolution 

 seems to be more moderate. 



With the recognition of but a single species in this genus, attention 

 need be paid only to the status of the three geographic races of C. 

 georgiana. 



That these three groups are conspecific is, I believe, obvious. While 

 remarkably dissimilar in appearance and probably unable to inter- 

 mate, C. g. georgiana and C. g. ducilla are nonetheless connected by a 

 broad zone of intermediate populations which bridge by small grada- 

 tions the gaps in all the diagnostic characters. The two named sub- 

 species are fairly constant over their ranges — as defined by the sum of 

 several characters taken in combination — but it has been sometimes 



2 Some may prefer to retain the name Zinaria Chamberlin, 1939, pending confirmation of the older Pleuro- 

 loma as the correct one for the genus. 



