162 Illinois State Laboratory of Natural History. 



spine in the middle, and ends in a short obtuse process, the 

 inner apical angle of which exhibits three small oblique in- 

 cisions. The inner margin is minutely ciliate. The inner 

 ramus is simple and slender, attenuate toward the apex, and 

 reaching about to the middle of the second segment of the 

 outer ramus. 



"Length of female, 2.3 mm. ; of male, 2.0 mm. 



"Found near San Francisco by G. Eisen. 



"This Diaptomtis approaches D. longicornis var. similis 

 Herrick in the shape of the body and of the lateral lobes of 

 the last thoracic segment, but it differs greatly in respect to 

 the fifth pair of feet, especially in the male. It seems to be 

 common in the vicinity of San Francisco, hence the name, 

 frauciscanus."* 



The female is conspicuous chiefly for the extremely long 

 spines with which the inner rami of the fifth pair of feet are 

 armed. These are about as long as the ramus itself and 

 hairy at the base. The thorax and abdomen are of ordinary 

 form. The furca are hairy within, and also, but more 

 sparsely, on the outer margin. In the male the outer margin 

 is not hairy. 



The outer ramus of the left fifth foot of the male is termi- 

 nated by a peculiarly flattened segment (PL XXX., Fig. 3). 

 In a male of this species sent me by Professor Lilljeborg, 

 both inner rami of the fifth pair of legs are two-segmented. 



Diaptomus eiseni Lilljeborg. 



Diaptomus eiseni, de Guerne et Richard, '89b, p. 44, PI. I., Fig. 19, 



29, 33.t 

 Diaptomus eiseni, Herrick and Turner, '95, p. 58, PI, X., Fig. 11. 



"Among the largest of the genus. Cephalothorax widest at 

 the posterior part of the head. The last two thoracic seg- 

 ments usually confluent above or indistinctly segmented, and 

 the lateral lobes of the last segment, seen from above, short 



*Lilljeborg"s description and remarks from de Guerne et Richard, '89b. 



+ Confusion maybe caused by a slight mistal^e which crept into de Guerne and 

 Richard's "Revision." In the index and under the species names, Fig. 20, PI. I. is 

 given as the fifth foot of D. serricornis and also of D. eiseni. The "explanation of 

 plates' however, gives Pig. 29, PI. I., as that of I)- eiseni, which by comparison with 

 the description is found to be correct. 



