STATE GEOLOGIST. 



223 



water copepod known to me; it is a deep red in color and very com- 

 pactly framed. Although so much larger than D. castor, it is almost 

 impossible to find any structural differences. The male fifth foot dif- 

 fers somewhat, but mainly in the enlargement of one part afe the ex 

 pense of the others. The thorns on the feet are strongly pectinate 

 and the larger ones bear short spines instead of bristles. 



Diaptomus armatus, sp. n. 

 (See accompanying cut,) 



A second form is imperfectly known, but presents some clearly 

 marked distinctions which may have specific value. 



Length about as D. castor; body slender; antennaB reaching base of 

 abdomen only; female differing otherwise but little from B. castor (?); 

 male considerably smaller; caudal stylets narrow; antennae peculiar, 

 shorter than the body; thickened portion of the geniculate antenna 

 short; two last joints very short; one preceding the second long, bear- 

 ing a hook at end; fifth foot with a very long claw to longer ramus 

 (nearl}^ as long as the ramus itself) with a tooth on the inner margin 

 near the base, not perfectly arcuate, reaching, when extended, to end 

 of caudal setse. 



Pig. 1. 



Diaptomus armatus. 

 a. part of male antenna, b. fifth foot of male. 



Genus potomoichetoe,* Gen. nov. 

 Cephalothorax six-jointed as in Diaptomus, but with the distal seg- 

 »ient more evident; abdomen, in the male, five-jointed, in the female 



•River iuhabitor. 



