8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 6l 



The species is so clearly distinct from other species that it has 

 seemed best to give the description in spite of the fact that the females 

 are unknown. 



Pscudodiaptomus cristobalensis was found in the collections made 

 in the old French canal, in salt and brackish water, and has been 

 given tins specific name as it may be considered characteristic of the 

 brackish water of the Atlantic side of the isthmus. It seems probable 

 that further collections will bring to light at least one other species 

 of this genus. 



DIAPTOMUS GATUNENSIS, new species 



A small species. The first cephalothoracic segment is about twice 

 as long as the second. Each of the succeeding segments is slightly 

 shorter than the one anterior to it. The last cephalothoracic segment 

 is armed with an acute spine on each side (pi. i. fig. 9). and has on 

 the posterior border of each side about three small blunt spines. The 

 general form of the cephalothorax is a narrow oval. The dorsal 

 surface of the fifth cephalothoracic segment near its posterior border 

 is thickly covered with minute spines. These spines are much more 

 numerous in the female than in the male. 



The first segment of the female abdomen (pi. 2, fig. 7) slightly 

 exceeds the rest of the abdomen including the furca. It is dilated 

 laterally, its greatest width being to its length as about three to four. 

 It is armed on each side with an acute spine of moderate size. The 

 second segment is less than half the length of the third. The furcal 

 rami are somewhat shorter than the third abdominal segment and 

 are ciliated on the inner margin. 



The antennae reach considerably beyond the end of the furca. The 

 right male antenna is swollen anterior to the geniculating joint ; the 

 antepenultimate segment has a hyaline lamella extending its length 

 and projecting from its distal end in a blunt point (pi. 2, fig. 10). 



The spines of the first basal segments of the female fifth feet (pi. 

 1, fig. 8) are large and prominent. The lateral hair of the second 

 basal segment is of usual size. 



The first segment of the exopodite is about twice as long as wide. 

 The second segment, with the hook, is nearly as long as the first 

 segment, and bears a rather small spine on its outer distal angle. 

 The inner margin of the hook is finely denticulate. The third seg- 

 ment is distinct and bears two slender spines, the inner of which i^ 

 nearly twice as long as the outer. The endopodite is composed of a 

 single segment, is about one-half as long as the first segment of the 

 exopodite. and has inconspicuous setae near the tip. 



