880 THE AMERICAN NATURALIST. | [Vor. XXXIV. 
sculptured into rhombs and prolonged posteriorly into a long 
dorsally directed spine (Fig. 1). 
Observers subsequent to Leydig failed to find this species, 
but described forms which resembled it in all points excepting 
the form of the crest. The deviations here were sufficiently 
great to lead to "mer classification as distinct species. Such 
were D. gracilis Hellich, D. pel- 
lucida Müller, and D. galeata 
Sars ; and not until recent years, 
when forms transitional between 
them and D. hyalina were found, 
have these come to be regarded 
as varieties of D. hyalina. 
Of D. galeata, Sars (63) said : 
“It is distinguished from all 
other forms by the very char- 
acteristic development of its 
crest, which projects forward in 
an acuminate apex, giving the 
head a certain likeness to a hel- 
met of the olden time. This 
singular projection undergoes 
noticeable variations in different 
localities. Sometimes it takes 
a direction straight forward, 
sometimes it is bent downward, 
Fic. 1.— Daphnia hyalina Leydig; mn.,mac- and again it is very short, 
M Acre ad |^e.tmim! almost disappearing in adult 
females. In other localities the 
apex is highly developed, sabre-pointed, and in some even 
slightly recurved." The writer, however, fails to note a resem- 
blance between any of these varieties and D. hyalina. In his 
résumé of thé characters of D. pellucida, Müller (68) makes 
mention of a pectinated terminal claw on the telson, which, 
if it is anything more than the fine striations noticed by Leydig, 
would serve to separate the two species ; but later, in his * Clado- 
ceres des Grand Lacs de la Suisses," he identifies Pellucida 
with Hyalina, since he found * all transitions between D. yalina 
