162 Trans. Acad. Sci. of St. Louis. 
All who have had a first-hand acquaintance with Daph- 
mia hyalina have noticed the marked morphological differ- 
ence of individuals captured from the same pond. In 
some the head bears a spine, in others it does not; in some 
the dorsal spine is short, in others it is long; in some 
cases the spine is at the dorso-caudal angle of the shell, 
in others it is lower down. Heretofore, so far as my 
knowledge goes, these forms have been considered indi- 
vidual peculiarities, distinct varieties, or even distinct 
species. The relative length of the spine is apparently 
an individual matter, at least its relative size is not deter- 
mined by the age of the animal. In.the forms that are 
found around Augusta, the other differences are differ- 
entiations due to age. In the young embryo in the brood 
pouch, the caudal spine is so bent down and appressed 
against the body that the posterior border of the body 
appears to be rounded (Pl. XXXVII. f. 1) or slightly 
pointed (Pl. XX XVII. f. 2) and the head is spineless. 
The free swimming but immature form has a long caudo- 
dorsal spine and a short, but prominent, head spine (PI. 
XXXVII. f. 3); in this stage the body is relatively quite 
long. Between now and the breeding stage, the body 
becomes relatively much higher; otherwise there is no 
marked change, except, perhaps, a slight shortening of 
the spine on the head (Pl. XXXVII. f. 4-5). When the 
animal begins to breed, the long spine on the posterior 
border progressively retreats ventrad; this is due to the 
enormous development of the brood sac (the old female 
bearing fully three times as many eggs as the youngest 
breeders—Pl. XX XVII. f. 6-8). In old forms the spine 
on the head disappears entirely (Pl. XX XVII. f. 8). 
BOSMINA Baird. 
25. BOSMINA LONGIROSTRIS O. F. M. 
Bosmina longirostris, Birge, ’78, p. 15. 
Bosmina longirostris, Herrick & Turner, ’95, p. 207; pl. XLV., fig. 
Be Di ida, Gee 2. 
This form was abundant in the temporary portions of 
a large no-outlet pond, at a water temperature of 21° ye 
