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Discussion
I have identified this specimen as Vibilia stebbingi with considerable trepidation. The numerous species of Vibilia appear from the literature to be very much alike, at least in detail. It may be that the lack of distinguishing characteristics which makes me hesitate to identify this specimen with any one particular species is not borne out in gross facies (cf. species of Parathemisto and Cyllopus) so that the different species may be more easily distinguished when one has a range of species material for comparison.
Pirlot (1929) gives a key based on Behning's (1913) which is somewhat difficult to use because one or two of the more important dichotomies do not seem to me well defined and because the features referred to are not figured in descriptions of the species. For example, V. antarctica and V. propinqua are separated from V. stebbingi and V. viatrix as follows: “distal extremities of the sideplates of the 1st ural segment completely rounded, without ornamentation” in V. stebbingi and V. viatrix, and “finely toothed” in V. antarctica and V. propinqua. Since these particular characteristics do not seem to have been figured for any of the species, there is no real indication of how distinct the teeth are.
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If, as I take it, my specimen lacks them, then it falls into the first complex. In that case, it agrees closely with V. stebbingi in the uropods and, as Stephensen (1918) suggests, is easily distinguished from V. viatrix. The inner side of the outer ramus of the first two uropods has large teeth distally, small ones proximally, whereas in V. viatrix the teeth are of equal size throughout. The antennae agree perfectly with Behning's figures. But the second gnathopod carpal process reaches the dactylos, characteristic of V. antarctica which falls into the other dichotomy. It is not mentioned as characteristic of V. stebbingi—indeed all figures show it at most ⅔ the propod length. And although the original descriptions of V. viatrix show a similar short process, Shoemaker's figures (1945) show the process as in my specimen which agrees with V. viatrix in several other points. The fifth peraeopod agrees closely with Behning's for V. stebbingi. The third and fourth agree much more closely with V. antarctica—so much so that I would not be surprised if eventually the specimen proved to be V. antarctica, which has similar uropods to V. stebbingi.
When specimens separated by the key into one dichotomy appear in all other characteristics to belong to the other, one begins to doubt the validity of the diagnostic features concerned. However, if my specimen is mature, the size ranges which Barnard gives (1930) suggest V. stebbingi, to which I refer it very doubtfully.