4 U.S. NATIONAL MUSEUM BULLETIN 259 



Barnard, 1958, for synonyms), although Mohi- as recently as 1948 

 made reference to Eucrangonyx jiagellatus (Mohr, 1948). 



Greaser (1934), under the false impression that S. jiagellatus had 

 an inner ramus on the third uropod, described the genus Synpleonia 

 (type species =»S'. clantoni) on the basis of material collected from a 

 well in eastern Kansas. He mistakenly pointed out that his new 

 genus {Synpleonia) differed from Stygonectes in two important char- 

 acters — by lacking an inner ramus on uropod 3 and by having all 

 three uronites coalesced (only uronites 2 and 3 were considered to be 

 coalesced in Stygonectes) . Mackin (1935) added further to this con- 

 fusion by describing another new stygonectid amphipod from Okla- 

 homa and assigning it to the otherwise monotypic, European genus 

 Boruta (B. americana Mackin, 1935). Shortly after this, however, 

 Boruta was synonymized with Synurella (Schellenberg, 1936). While 

 Mackin (1935) observed that Boruta americana was closely allied to 

 Stygonectes jiagellatus, he indicated that these forms differed from 

 each other in the extent of fusion of the uronites (pointing out that 

 in Boruta all three m-osomal segments were fused as in Synpleonia), 

 and that the former lacked an inner ramus on the third uropod. It 

 is apparent that neither Greaser nor Mackin ever consulted the type 

 material of Stygonectes jiagellatus, or else they would have realized 

 that this species did not possess a biramous third uropod as originally 

 and erroneously reported by Weckel (1907). 



Schellenberg (1936) resolved some of the problems which had 

 plagued American amphipod workers but did not completely resolve 

 all of them. Schellenberg relegated both S. Jiagellatus and iS. tenuis 

 to Stygonectes, and in his diagnosis of this genus the third uropod 

 was shown to be uriramous; but in the same paper he maintained 

 generic separation of Stygonectes and Synpleonia and assigned Crang- 

 onyx alabamensis, Synpleonia clantoni, and Boruta americana to the 

 latter. From Schellenberg's diagnoses of these two genera one was 

 led to beUeve that they differed only in degree of fusion of the uronites. 

 In a paper describing Synpleonia pizzinii. Shoemaker (1938) rightly 

 pointed out that all three of the uronites may or may not be coalesced 

 in either Stygonectes or Synpleonia. Also, he correctly emphasized 

 that what appeared in some specimens to be an articulation between 

 urosomal segments 1 and 2 was only a shallow depression that varied 

 to the extent that in some specimens it appeared to be a true articula- 

 tion, while in others it was scarcely perceptible. Shoemaker further 

 pointed out the remarkable similarity between species in Synpleonia 

 and Stygonectes, but he failed to unite the two genera on the premise 

 that in species of the former the lateral sternal gills were bifurcate, 



