THOMPSON: A RAKE THALASSINI1). 
7 
5. Fifth pereiopod not rudimentary; pleopod rudiments large. 
Length, 9.3-10 mm. (pi. 2, fig. 23). 
No specimens of these stages were collected in 1901 until the 
latter part of August, but last summer some first and second stages 
were taken as early as the middle of July. The first third stage 
larva was found about a week later. No fourth stage, however, 
was collected before the second week in August, and fifth stages 
not till near the end of the month. Such data indicate that the 
rate of development is slow, but cannot be relied upon for an 
accurate estimate. 
The external structure and “habitus ” during these stages are, as 
already rioted, quite unusual. They have a dark brown coloration 
due to numerous dendritic chromatophores of that color combined 
with more diffused yellow pigment. The dark chromatophores 
cover the ventral face of the antennulae and abdomen and are more 
scatteringly distributed along the bases of the appendages. The 
yellow pigment is diffused over the eyes, antennulae, bases of 
appendages, rear of carapace, sides and venter of abdomen; and a 
single chromatophore occupies the apex of the proximal joipt of the 
two anterior maxillipeds. The carapace is smooth, and is produced 
forward of the mandibles into a short “neck.” The abdomen is 
without carinae or spines, but the outer angles of the second to the 
fifth segments are modified to form arcuate processes, and the 
angles of the telson are elongated. Arcuate processes are not 
developed on the sixth segment in any stage, and only imperfectly 
on the first segment in the earlier stages. The abdomen makes up 
one half of the total length in the first stage, but becomes propor¬ 
tionately longer in the later stages, finally being twice as long as the 
carapace. The free spines on the border of the telson are 10 in 
number in the first; 14 in the second ; 14 or 15 in the third ; 14 
to 16 in the fourth; and 15 in the fifth stage. In the later stages 
one of the innermost pair is frequently much smaller than its 
fellow. 
The mandibles (mnd) are similar in structure in all stages, but 
deserve especial attention because of their asymmetry. The one on 
the left (pi. 3, figs. 32, 34, 35) is arcuate and on the inner surface of 
its base are two stout teeth and within these an erect, serrate plate 
(pro). There is no palpus rudiment. The mandible of the right 
side (pi. 3, figs. 31, 33) is conical and the inner surface of the base 
