Birge—Notes on Cladocera. 
1049 
tinct section of the genus. He added later (’01) the species 
lineolata, sculpta (—globulosa Daday) and dentifera. These 
are accepted by Daday (’05) as belonging to Alonella. 
Daday (’05) placed A. mstrata in the genus Leptorhynchus 
Herrick, a genus established for the form Alona (LLarpor- 
hynchus ) falcata. He added a new species L. dentifer , which 
is closely related to A. nana. This change seems to make for 
confusion rather than order. Leptorhynchus falcatus (G. O. 
Sars) with its peculiar form, extremely long rostrum, and its 
unique postabdomen, is very different from either of the 
species with which Daday seeks to unite it. It appears to be 
as well defined a genus as any of the other monotypical genera 
of Chydorina, such as Graptoleberis. 
This sketch, which does not pretend to be exhaustive, shows 
that on the one hand authors have recognized the difficulty of 
limiting and defining a genus Alonella, to which to assign the 
species in question, and on the other hand have found it hard 
to place these species in other genera or to separate them from 
each other. It seems to have been largely a matter of per¬ 
sonal choice and of convenience whether these species shall 
be doubtfully attached to other genera, or doubtfully put to¬ 
gether in a single genus, but on the whole the tendency has 
been to follow Sars in recognizing a genus Alonella as an as¬ 
semblage of forms, widely differing, yet so interrelated as to 
be inseparable; closely related to other genera yet not readily 
included in them. In my synopsis of the Cladocera of the 
United States, I have chosen the latter alternative. I recog¬ 
nize that the genus is not such in any proper sense. The spe¬ 
cies included in it have so few common peculiarities that no 
good definition can be framed. It may be divided into three 
subgenera, as follows: 
a. Alonella proper. Rostrum long, slender, recurved; al¬ 
ways much exceeding antennules. Postabdomen with mar¬ 
ginal denticles only; claws with one basal spine. A. rostrata 
(Koch) ; A. nana (Baird) ; A. dadayi Birge (= Leptorhynchus 
dentifer Daday). The specific name of the last species must be 
changed from that given by Daday if it is to be included in 
Alonella; as dentifera was already employed by Sars: 
