298 
Birge—Notes on Cladocera. 
gether in these collections in much the same way as D. hyalina 
and D. recrocurva, are apt t'6 do. Their numbers, however, are 
more nearly equal, and in some bottles D. microcephala may be 
the more numerous. 
In general form this species closely resembles D. longiremis. 
The valves are perhaps somewhat more elongated, but still are 
of a broadly eliptical form. The spine projects near the middle 
of the shell and extends nearly straight backward. It is beset 
with few and very small spinules. I see no difference between 
j D. longiremis and D. microcephala in these respects, although 
Sars’ description indicates one. 
The head is small; its height is about one-half that of the 
valves and its free projection is less than its height. It has a 
slight keel on its dorsal side, which is wider on the anterior 
edge. Seen from the side, the head is usually evenly rounded 
in front but occasionally there is a trace of angulation. There 
is never an indication of a projection or spine. The ventral 
margin of the head is straight and rounds over smoothly at the 
posterior angle. There is practically no rostrum. The sense- 
hairs of the antennule project below the ventral margin of the 
head. 
The antenna is moderately stout, having about the proportion 
of that of D. hyalina. The seta of the basal joint of the ven¬ 
tral ramus is about as large as its fellows. The eye is of mod¬ 
erate size and of the type seen in D. hyalina , having a moder¬ 
ately large amount of pigment. The material at command is 
not so preserved as to show the other internal organs. 
The postabdomen is long and slender. It bears about nine 
anal teeth. The caudal claws have the usual two spinules on 
the anterior ventral side and are denticulate. The first and 
second abdominal processes are slightly united at the base. 
The second process is about one-half as long as the first. 
Liength 1.3-1.5 mm., including spine. 
The descriptions of this species given by Sars and Hellich do 
not quite agree. The former speaks of a small macula nigra 
{’63, p. 22.) while Hellich (77, p. 37.) did not find that struc¬ 
ture. He saw the species only once. I have been unable to see 
the macula nigra, but the condition of the material is such that 
