82 



strong, partly ciliated setae. Posterior antennae with all the joints well defined, 

 the terminal one very short, scarcely more than half the length of the penulti- 

 mate one. Maxillipeds short and stout, the posterior ones, however, somewhat 

 more fully developed than in the 2 preceding species. Natatory legs resembling 

 in structure those in P. phaleratus; apical spine of inner ramus in 1st pair, 

 however, comparatively larger; those in 4th pair rather unequal, the inner one 

 being about twice as long as the outer. Last pair of legs well defined, resembling 

 in structure those in P. affinis: spine of inner edge, however, considerably shorter. 

 Ovisacs in some cases rather large, oblong oval in form, and closely appressed 

 to the tail. Seminal receptacle rather broad, transversely elliptical in form. 



Colour whitish, with the ovarial tubes dark bluish; eggs in the ovisacs 

 generally of a similar dark hue; eye bright red. 



Length of adult female about 0.90 mm. 



Remarks. This form was at first identified by me with Cyclops crassi- 

 cornis of 0. Fr. Miiller; but it is very questionable if the form so named can 

 be assigned to the present species, or even to the genus Cyclops. Fischer's 

 description, on the other hand, does not leave any doubt about the identity of 

 his species with that here in question. It may be easily recognised from either 

 of the 2 preceding species by the short and thick anterior antennae, and the 

 rather different shape of the caudal rami. 



Occurrence. I have met with this form only occasionally in small ponds 

 and ditches, more frequently in larger lakes, where in some cases it descends to 

 rather considerable depths. Thus in Lake Mj0sen I have taken it in depths 

 down to 50 fathoms. Like the other species of this genus, it is a true bottom- 

 form, always keeping close to the ground. 



Distribution. Sweden (Lilljeborg), British Isles (Brady), Germany (Schmeil), 

 Poland (Lande), Russia (Fischer). 



Section 2. Siphonostoma. 



General Characters. Anterior antennae in male generally (but not always) 

 geniculatei. Posterior antennae, as a rule, provided with a very small uniarticulate 

 appendage as the rudiment of an outer ramus. Oral parts not adapted for 

 mastication, the anterior and posterior lips being generally produced to form a 

 prominent cone, terminating in some cases in a long siphon. Mandibles with 



