122 TWELFTH ANNUAL KEPORT. 



Si>, 2. Polyphemus stagiialis. (Sp. n.) 



In order to make the relation clear between these forms, I add 

 measurements of this species, followin^^ each with the correspond- 

 ing measurement of P. pediculus in parenthesis; animals of the 

 same age, as far as possible, being chosen. Head (capsule of eye) 

 0.3 mm. (0.2 mm.); head and thorax 0.7 mm. (0.45 mm.); abdomen 

 O.T mm. (0.56 mm.): caudal stylet 0.36 mm. (0 26 mm.); caudal 

 filaments 0.36 mm. (0.3 mm.). Whole length of antennae O.oi mm. 

 (0.42 mm.); first, second and third joints of the 3-jointed ramus 0.08, 

 0.06 and 0.10 mm., respectively. The formation of the resting eggs 

 or "dauer-ei" seems to go on at the same time with the partheno- 

 geuetic reproduction. 



II. — Genus Bythotrephes, Leydig. 



Much like Polyphemus, but the external appendage of the feet is 

 rudimentary, and the abdomen extends out into a most enormous 

 spine. The single species is that described by Leydig as B. longi- 

 manus, which was found in the stomach of Coregonus wartmanni. 

 B. cederstromii, of Schoedler and P. E. Mueller, the latter author 

 now identifies with the above, and concludes that the supposed 

 differences arose from "I'etat de maceration des examplaires exa- 

 mines." (Les Cladoceres des Grands Lacs de la Suisse, p. 11.) 

 This species may be looked for in the depths of the Great Likes. 

 (See plate U, fig. 10.) 



III. — Genus Podon. 

 IV. — Genus Evadne. 



These are compact oval forms confined to the sea. See Claus, 

 Zur Kenntniss des Baues der Pohjphemiden, Vienna, 1877, for the 

 best account of the anatomy. 



FAMILY LEPTODORIDyE. 



Feet six pairs. Antennae with both rami four-jointed. Body 

 elongated, not curved, shell very much reduced. 



