52 Rowland M. Shelley 



podite section in Shelley 1981a) or the proximal locations of the medial 

 flanges, which originate on the basal zones in shelfordi and arcuatus. 

 Although an inappropriate name, however, Brevigonus was validly pro- 

 posed and must be retained for the taxon encompassing these two 

 species. 



There are positive aspects to the belated inclusion of arcuatus in 

 Brevigonus. Improved diagnoses of the genus and of shelfordi are now 

 possible, and certain anatomical features of shelfordi can now be more 

 accurately interpreted. Moreover, arcuatus evinces a close relationship 

 between Brevigonus and Sigmoria as opposed to one between Brevigo- 

 nus and Cleptoria as previously stated (Shelley 1980). The significance 

 of the flange on the medial surface of the acropodite, for example, was 

 not evident when shelfordi was studied alone, because the shortened 

 acropodite of this species terminates at the peak and lacks the distal 

 zones and apical curves present in arcuatus and species of Sigmoria. 

 Brevigonus shelfordi is thus a modified species that lacks the distal 1/3 

 to 1/2 of the normal apheloriine acropodite. Consequently, the medial 

 flange of shelfordi did not previously show any resemblance to the 

 flanges of certain species of Sigmoria, but the similarity is obvious in 

 arcuatus, since it possesses the distal sections of the acropodite. Brevi- 

 gonus can now be partly defined as an apheloriine genus with a flange 

 on the medial face of the acropodite, arising on the proximal portion of 

 the basal zone and terminating on the proximal portion of the peak. It 

 differs from Sigmoria in the more proximal location of the flange, 

 which is located on the peak (arising at the anterior bend) or the distal 

 zone in this genus. The flange is variable in Brevigonus and is reduced 

 or vestigial in individuals of both species. The margin is also irregular, 

 and the flange may extend straight across the anterior bend as shown in 

 Figure 3, or curve parallel to the acropodite stem as shown in Figures 

 8-9 of shelfordi in my 1980 paper. The apparent distal lobes on the 

 acropodites of the latter individuals can now be recognized as the ter- 

 mination points of the medial flanges, which end on the distal portions 

 of the acropodites in shelfordi only because this structure is shortened. 

 Thus by clarifying the significance of the medial flange, arcuatus reveals 

 a close phylogenetic affinity between Brevigonus and Sigmoria, which is 

 confirmed by one other character — the reflexed tips on males in the 

 southern part of the range of arcuatus. These individuals, from Abbe- 

 ville County, South Carolina, have reflexed tips identical to those of 

 certain species of Sigmoria, for instance S. latior (Brolemann). No other 

 apheloriine taxa in the southeastern Atlantic lowlands display this ter- 

 mination of the acropodite, and its presence in species of Sigmoria and 

 Brevigonus is strong evidence of a close relationship between the two 

 genera. No such evidence exists of a relationship between Brevigonus 

 and Cleptoria. My comments to this effect in 1980 were based on what I 



