314 BULLETIN OF THE 
become divided by a transverse suture near its base, so that it now 
consists of two segments, a short proximal and a long, slender, distal 
one. The external branch of the second antenne (Pl. II. Fig. 5, ZZ, 
r e) has increased in size, but otherwise has suffered little modification. 
The posterior border of the labrum, which bounds the mouth in 
front (Pl. II. Fig. 7), when viewed under a high magnifying power is 
seen to be serrate with minute teeth. 
The mandibles and maxilla (Pl. II. Figs. 5, 8, 9) have undergone little 
change. 
A fifth pair of swimming-feet (Pl. II. Fig. 5, X) has developed from 
the anterior of the sac-like buds behind the last pair of swimming-feot 
of the preceding stage. This pair of swimming feet corresponds to the 
second or larger pair of chelipeds of the adult Palcmonetes. They aro 
similar in make to the preceding pairs, but somewhat shorter. "The 
antecedent pair of swimming-feet have gained in length, so that they 
now equal, if they do not slightly exceed, the pair in front of them. 
The segmentation of the inner branches of all the swimming-feet is more 
distinct than at first, dividing them into four segments, at least in the 
hindmost three pairs. 
A new pair of sac-like appendages (Pl. II. Fig. 5, X7/1) have devel- 
oped behind the swimming-feet, so that we still have two pairs (XJ and 
XII), which will disclose swimming-fect after the next moult. The 
gills have begun to develop at the base of the swimming-feet. 
The broad triangular fin which terminated the abdomen in the last 
stage has by exuviation freed the posterior pair of abdominal append- 
ages (Pl. IL. Fig. 5, XIX), of which we have seen the rudiments 
through the transparent integument in the previous stage. Both 
branches of these appendages are developed as two oval plates, of which 
the outer is two thirds the length of the telson, the inner about one 
third. The larger plate is fringed with fine sete on its inner, and on 
the hinder portion of its outer, border. The telson itself, as before said, 
is much narrower than before, and is separated by a suture from the 
sixth abdominal segment. Its hind margin now bears but twelve long 
sete, the external one on each side having disappeared. 
On the lower side of the thorax, between the bases of the swimming- 
feet, is a good deal of green pigment beautifully arranged in dendritic 
figures, Other parts of the body also are rendered conspicuous by spots 
of red, green, and yellow. 
Length, 3.5 mm. 
Fourth Larval Stage (Pl. II. Figs. 10-15; PL III. Figs. 1 - 3). — At 
