Birge—Notes on Cladocera. 
1019 
its junction with the flagellum. Of this sketch, however, he 
made no use, hut the published figure shows the position of the 
olfactory setae, which is important in characterizing the genus. 
There is no difficulty in identifying the specimens belonging 
to this species from Herrick’s plate and description of 1884. 
I found no specimen of P. tridenta or tridentata; but some 
light, though unfortunately not as much as could be wished,, 
has been thrown on the subject by Stingelin’s discovery (’06) 
of two poorly preserved specimens from Paraguay, which seem 
to belong to the species. Stingelin is undoubtedly correct in 
stating that Herrick in his Pseudosida tridentata had a dif¬ 
ferent species from that which he had formerly described un¬ 
der the name hidentata. The drawings of this species are 
contained in a different note-book, also undated, but labeled 
“Later Gulf of Mexico, etc.” The sketches do not contain 
any drawing of the species as seen from the side. In this 
particular Stingelin’s remark is instructive, that the species, 
unlike P. szalayi, does not naturally lie on its side when 
placed under the microscope. I found that P. hidentata, like 
Bida, and unlike Latonopsis, does lie on its side. Herrick 
gives no sketches which tvould aid in the identification of the 
form, more than the published drawings do. The only im¬ 
portant difference between the sketches and the published 
drawings lies in the antennule, which in the engraving (’87, 
PI. Ill, fig. 3) shows a gradually tapering connection between 
the basal part and flagellum. This is not present in the sketch 
and is no doubt an error made in copying the sketch. The 
postabdomen is also broader and blunter in the sketches than 
in plate III, fig. 4. Mr. E. Foster of Hew Orleans has sug¬ 
gested to me that possibly Herrick had before him Latonopsis 
fascicnlata Daday—a form which Mr. Foster has found at Hew 
Orleans and which-1 have also found in other localities in the 
south. So far as most of the details of structure are concerned, 
this is not improbable; but the outline of the animal, as seen 
from above, does not suggest Latonopsis , nor is the postabdomen 
similar. Future investigation will be necessary to decide with 
reference to the form represented by P. tridentata. It may 
well be that the species which Herrick had is the same as that 
