A New Milliped of the Genus Brevigonus from South Carolina, 



with Comments on the Genus and B. shelfordi (Loomis) 



(Polydesmida: Xystodesmidae) 



Rowland M. Shelley 



North Carolina State Museum of Natural History, 



P.O. Box 27647, Raleigh, North Carolina 27611 



ABSTRACT. — Brevigonus arcuatus, new species, is characterized by 

 a broadly curved acropodite in which the distal zone is moderately 

 long and possesses either simple or reflexed tips. Its congener, B. shel- 

 fordi (Loomis), is distinguished by absence of a distal zone and apical 

 curve, and its abbreviated acropodite terminates at the distal extremity 

 of the peak. An improved generic diagnosis is possible. Brevigonus is 

 characterized by the spine at the base of the acropodite, and by the 

 proximal location of the medial flange, which arises on the basal zone 

 and ends on the peak and separates Brevigonus from the related genus 

 Sigmoria. 



In 1980 I attempted to dispose of a long standing taxonomic prob- 

 lem in the Xystodesmidae by erecting the new genus Brevigonus for 

 Cleptoria shelfordi Loomis. Hoffman (1967) removed this species from 

 Cleptoria but did not assign it to another genus. Before publication I 

 collected extensively in and near the range of shelfordi, the north side of 

 the Savannah River in the Piedmont Plateau of South Carolina, to try 

 to discover other species for this genus. Finding none, however, I reluc- 

 tantly concluded that there was no alternative to a monotypic taxon. 

 Two basic gonopodal variants of shelfordi were at hand, but they 

 clearly were not reproductively isolated. Consequently, I proposed the 

 genus Brevigonus to emphasize what I considered the most distinctive 

 feature of shelfordi, its shortened gonopodal acropodities. 



I did not know in 1980, however, that a form I was referring to 

 Sigmoria was actually closely related to shelfordi. I had collected this 

 species several times in piedmont South Carolina but had assigned it to 

 Sigmoria because of the overall curvature of the acropodite. Not until I 

 was well into revising Sigmoria did I realize that this species was conge- 

 neric with shelfordi, and by that time the Brevigonus paper had been 

 published. The new species shares several features with shelfordi that 

 make for a sound generic diagnosis, but shortness of the gonopodal 

 acropodites is unfortunately not one of them. This trait is a specific 

 characteristic of shelfordi', the acropodites of the new species are long 

 and form a broadly curved arch, which is the basis for its specific name, 

 arcuatus. Brevigonus was thus a regrettable choice for a generic name, 

 since it is based on a derived character of only one species and not on a 

 trait shared by all components of the genus. A better name would have 

 emphasized the spines on the basal zones (see terminology of the acro- 



Brimleyana No. 6: 51-60. December 1981. 51 



