MUSEUM OF COMPARATIVE ZOOLOGY. 263 
III. Pinnixa. 
As long ago as 1835 the zoéa of Pinnotheres was raised from the egg and 
figured by J. V. Thompson.* Although this was one of the earliest known 
cases of metamorphosis among the Orustacea, Thompson's memoir has remained 
the sole contribution to the developmental history of the Pinnotheride up to 
the present time. 
In the latter part of August, 1878, a large zoéa was not uncommon in Narra- 
gansett Bay, which developed in the aquarium into a species of ۸ 
The development of this species is remarkable for the complete suppression of 
the megalopa-stage, the zoéa figured on Plate IV. (Figs. 5-15) passing directly 
into the first stage of the crab, represented on Plate V. 
In the last zoéa-stage (Plate IV. Figs. 5-15) the carapace is armed with 
long frontal, dorsal, and lateral spines. The natatory feet are very short in 
proportion to the size of the body, the inner branch of the second pair (Fig. 11, 
a) rudimentary, as usual with Brachyuran zoëæ. The third pair of maxillipeds 
and the five following pairs of thoracic feet are folded under the carapace. 
On dissecting them out from the body, they are seen to be quite perfectly 
formed, as shown by Fig. 7. The third maxillipeds (Fig. 8) possess their 
three constituent parts (a, b, c) and a gill (d) at their base. 
The abdomen (Fig. 10) is short, its penultimate segment expanded laterally 
into two lobes, which extend backward on each side of the terminal segment. 
The terminal segment is ovate, produced posteriorly into a long spine on either 
side. Between the lateral spines and a small median sinus are three short, 
finely feathered set; on either side. 
There are four pairs of simple abdominal appendages. 
There is a black pigment spot at the base of the dorsal spine, one near the 
base of each of the lateral spines, and several on the abdominal somites. 
From tip of frontal spine to posterior border of carapace, 2.5mm. From 
tip to tip of lateral spines, 2 mm. Length of frontal spine, 1 mm. 
In the first crab-stage (Plate V.), which immediately follows the last zoëa- 
stage just described, the carapace measures less than 1 mm. in length by 1.5 mm. 
* Memoir on the Metamorphosis and Natural History of the Pinnotheres or Pea- 
Crabs. By W.[J. V.] Tompson, F. L. S. Entomological Magazine, Vol. III. pp. 
85-90. Figs. 1, 2. April, 1835. 
T This peculiarity is also seen in the undetermined zoéa, figured by Claus, “ Un- 
tersuchungen,” etc. Taf. XIV. Figs. 1, 2 (p. 65). The abdomen of the zova of 
Pinnotheres pisum apparently has a like form, judging from Thompson's rude figures 
(7. c), in which the penultimate and ultimate segments are represented as a single 
piece, 
In “ Für Darwin ” Fritz Müller figures the tail of a Pinnotheres (Fig. 19). Tt has 
the shape generally seen in Brachyuran zo&e, while Fig. 22, “of unknown origin,” 
represents a tail like that of Pinniwa and Thompson's Pinnotheres. Is there no con- 
fusion here ? 
