THOMPSON: A RARE THALASSINID. 
9 
two stages and become biramous with the third stage. The exopods 
are functional in the fourth stage. When functional, exopods of all 
the pereiopods resemble those of the third maxilliped. The fifth 
pair of limbs (o) is uniramous throughout the larval period. Gills 
appear in the fourth stage with the rudiments of all the arthro- 
branclis and a single common rudiment for the mastigo- and podo- 
branchs of each segment except /, m, and n. These are introduced 
with the fifth stage (pi. 2, fig. 30). The pleopods are introduced 
on segments two to five with the fourth stage and remain rudi¬ 
mentary during the following stage. They are biramous. The 
uropods enter with the third stage. 
Although a fairly large number of young Naushonia was obtained 
both in 1901 and in the past summer, it has not been possible to 
study the internal anatomy in detail owing to difficulties in tech¬ 
nique usual to the study of Crustacea. The results that have been 
obtained, however, show that in most respects the anatomy does not 
differ from that of other Decapod larvae. The stomach is laterally 
compressed, much deeper than broad, with a weak dorsal tooth, lat¬ 
eral teeth which project upward rather horizontally, and the cardio- 
pyloric and median pyloric valves, (the two latter being apparently 
confluent in the first stage). From at least the second stage on, 
the lateral teeth and the median pyloric valve end posteriorly in 
short, slender spurs so that, with the dorsal valve, there are four 
pyloro-intestinal valves. The lateral teeth and median pyloric 
valve are setose from the second stage, but the cardio-pyloric valve 
remains smooth until the third stage. Lateral pyloric pouches are 
introduced with the second stage, and oesophageal plates with the 
fourth stage. The stomachal musculature is simple, consisting, as 
in other zoeae, of dorsal and ventral supporting muscles. The 
intestine shows no chitinous lining until the middle of the sixth 
abdominal segment is reached. The cells of this achitinous part 
(int) — presumptive midgut— are short for the greater portion of 
its extent, but become more columnar anteriorly. Their free bor¬ 
ders are rounded into the lumen. The chitinous gut (ch int) — 
presumptive postgut — has moderately long, columnar cells which 
are more vacuolated than the cells of the achitinous gut, and at the 
point of union with the latter, the cells form prominent ridges, 
the methoria. The livers are the only diverticula from the intestine 
in the preadolescent stages, and the cells which make up their 
