158 



THE AMEBIC AN NATURALIST 



[Vol. LIII 



naspides, etc., while the fossil "G-ampsonycliidaB" (e. g., 

 "Gampsonyx/* PalcEOcaris and Gasocaris) are nearer 

 the living genus Bathynella. Such fossil forms as Prcea- 

 naspides found in the Carboniferous rocks is extremely 

 like the living Anaspides which has apparently pre- 

 served many ancestral characters, but little modified, to 

 the present time. The Anomostraea are related to the 

 Leptostraca, but no forms intermediate between them 

 and the Leptostraca have yet been described, and it is 

 possible that the line of descent of the Anomostraea leads 

 back to the branchiopods through Leptostraca-like forms 

 not yet discovered. Superficially, at least, such slender 

 branchiopods as Yohoia tenuis, etc., resemble certain 

 members of the Anomostraea, and it is possible that the 

 slenderer, more cylindrical Anomostraea, such as Bathy- 

 nella, may have inherited the tendency toward the slen- 

 der form of body from anostracan branchiopods of the 

 Yohoia type. In Bathynella the eyes have become com- 

 pletely lost, but in Koonunga sessile eyes are found and 

 their presence suggests that sessile-eyed forms may have 

 developed from the Koonunga type. In Anaspides the 

 eyes are stalked. 



From ancestors occupying a position intermediate be- 

 tween the Anomostraea and Cumacea (and also related 

 to the Mysidacea) have arisen the lines of descent leading 

 to the isopod Crustacea, Insecta, and ''Myriopoda" (s. 

 1.). The Tanaidacea (Chelifera) which occupy a posi- 

 tion near the base of the isopod stem are very closely 

 related to the Anomostraea, Cumacea and Mysidacea, 

 and, together with the Isopoda and Amphipoda (which 

 are descended from ancestors very similar to them), they 

 might be included in the Anomostraca-Cumacea group; 

 but if the Isopoda-Amphipoda group is considered sepa- 

 rately, the Tanaidacea must be included in the latter 

 group, since their closest affinities are with the Isopoda. 

 The Amphipoda are quite closely related to the Isopoda, 

 and their ancestors may also have arisen from forms 

 intermediate between the Anomostraea and Cumacea 



