54 ' Description of Genera and Species. 



mountain lakes of Tasmania.' It was subsequently more fully described by W. T. 

 Caiman,- who showed its affinities to the Palaeozoic genera Acanthotelson Meek and 

 Worthen, Gampso7iyx Jordan and v. Meyer, and Palaocaris Meek and Worthen. The 

 members of this family evidently belong to the great Mysid branch of the Schizopoda, 

 but are evidently more nearly allied to the family of the Lophogastrida? than to that of 

 the Mysidaj. Both the Anaspidai and the Lophogastridaj seem to have branched off 

 from the great Mysid stem together, but to have afterwards developed along different 

 lines. One point of difference especially interesting to the describer of the fossil forms 

 is that in the former family the carapace has not grown backwards so as to cover any 

 of the last seven trunk segments (hence the present name), while in the latter it has done 

 so, and in one genus, Charalaspis, it even overlaps well on to the tail segments, although 

 in no case is it in direct fusion with any of them, but only covers them loosely. As 

 Thomson's name is based on the study of the living animal, it is here adopted in 

 preference to that of Gampsonychidce of Packard, based upon the study of imperfectly 

 preserved fossils. Anaspides must be looked upon as a surviving remnant of an old 

 family in which many extinct forms were much more specialised than the survivor. 



Genus PAL^OCAEIS Meek and Worthen, 1868. 



1868. Palceocaris. Proceed. Acad. Nat. Sc. Philadelphia, p. 48. 



Palaocaris scotica B. N. Peach. PL VIIL, figs. 1-5. 



1882. Palaocaris scoticus B. N. Peach, Trans. Eoy. Soc. Edin., vol. xxx., p. 85, 

 pi. X., figs. 10-lOh. 



There are many specimens belonging to this species in the collection of the Scottish 

 branch of the Geological Surve}-, besides those which furnished the material for the 

 description of the species. In that description I expressed the opinion that it was to 

 be looked upon as a lowly Schizopod, and a further study of the old material in the 

 light of Sars' Eepoi't on the Challenger Schizopods still further confirmed me in that 

 belief Since then the living Anaspides was discovered, and its description by W. T. 

 Caiman^ throws a flood of light upon the present genus and its allies, and makes the 

 belief a certainty. 



General Description. — ^The chief new structural points observed during the present 



' Trans. Linn. Soc. Zool. (2), vol. vi., p. 3. 



° Trans. Roy. >Soc. Edin., 1896, vol. xxsviii., p. 787. 



■'' W. T. Caiman. Trans. Roy. Soc. Edin., 1896, vol. xx.xviii., p. 787. 



