160 Illinois State Laboratory of Natural History. 



"This species, so remarkable from the peculiarities pre- 

 sented by the last thoracic and the first abdominal segments, 

 was found by the Swedish naturalist, Trybom, at Multrooma 

 Falls, Oregon." 



The above is the description as given by Dr. Lilljeborg 

 (de Guerne et Richard, '89b). It agrees with the specimens 

 sent me by himself, but I note a few additional details. 



The abdomen of the female, seen from above, is asymmet- 

 rical, as is also the last thoracic segment. The first abdom- 

 inal segment is dilated anteriorly, and posteriorly is produced 

 on the right to form a blunt, almost semicircular, process. 

 Seen from the side this is fin-shaped, and both this process 

 and the one on the last thoracic segment are penetrated by 

 muscles. The furcal rami are hairy within. 



In the male the peculiar form of the right inner ramus, 

 the extreme shortness of the left leg, and the very irregular 

 shape of its last segment are especially characteristic. The 

 spines on the first basal segment of each leg and the teeth 

 on the terminal segment of the right leg are also conspicuous 

 because of their great size. 



The peculiarity of a dorsal process is found, to my knowl- 

 edge, in but two other species: D. sanguineus Forbes, and D. 

 signieauda Lilljeborg. In the small size of the inner ramus 

 of the right fifth foot of the male, D. trybomi approaches the 

 male of D. sanguineus Forbes, D. minutus Lillj., and D. lin- 

 toni Forbes. 



De Guerne and Richard give Multrooma Falls as the 

 locality, which was probably intended for Multnomah Falls, 

 Oregon, although Prof. Lilljeborg in a personal letter also 

 gives the former spelling. 



Diaptomus franciscanus Lilljeborg. (PI. XXX.,Fig.l-4.) 



Diaptomus franciscanus, de Guerne et Richard, *89b, p. 45, PI. I., 



Fig. 12, 13, 34; PI. III., Fig. 23. 

 DiapUxmus franciscanus, Ilerriek and Turner, *95, p. 5S, PI. VIII., 



Fig. 12. 1G. 



"Larger and more robust than Diaptomus tyrreli. Cepha- 

 lothorax widest in the middle, and the last two segments 

 confluent above. Lateral lobes of the last thoracic segment 



