MUSEUM OF COMPARATIVE ZOOLOGY. 257 
On several warm, still mornings in August, 1878, the zoée of Porcellana 
swarmed in the streaks of smooth water on the edge of the tidal currents at the 
mouth of Narragansett Bay.* They are sluggish, and move either forward or 
backward. The little spines with which their enormously developed rostra are 
armed serve to accumulate the minute particles floating in the water to such 
an extent that the little creatures often become quite conspicuous by virtue of 
the load of dirt which they carry. 
Of the numerous specimens which I collected almost all were in the stage 
immediately preceding the youngest stage of the crab, into which they readily 
developed in confinement, and some of which were taken from the sea with the 
ZOCD, 
Specimens in the last zoéa-stage (Pl. IT. Fig. 1) measure about 16 mm. from 
the tip of the rostrum to the tips of the posterior spines of the carapace. The 
rostrum is 11 mm. long, the posterior spines 2.5 mm. 
Viewed from the side, the carapace is of a long oval form, extending forward 
as an enormous rostrum, and baekward into two horns eurved slightly down- 
ward at their ends. The rostrum is furnished with five rows of little spines 
disposed as shown in the cross-section (Pl. IT. Fig. 3). The posterior horns 
have a single row of spines below (Pl. IT. Figs. 2, 4). The first pair of an- 
tenn (PL II. Fig. 6) are composed of a long peduncle which is obscurely 
divided into two or three segments, At its base there is a slight enlargement 
which contains the auditory apparatus (a). The peduncle bears a blunt process 
(b), and a longer segment (c) which is furnished with several sensory threads 
(d). The second pair of antenna consist of a two-jointed peduncle, in the 
basal segment of which may be seen the orifice of the, renal organ (c). Of the 
two branches borne by the peduncle, the inner (a) is the longer, and within 
its transparent integument is seen the multi-articulate flagellum of the antenna 
of the crab, to be disclosed at the next moult. The outer branch (b) is styli- 
form, The mandibles have a many-toothed crown (PI. IT. Fig. 8), and the 
palpus is represented by a very small protuberance (a). The bilobed metas- 
toma is armed with short sete on the inner margin of each lobe (Pl. IT. Fig. 
9). The first pair of maxille consist of an inner lobe (Pl. IT. Fig. 10 a) and 
* [ am indebted to Mr. Agassiz for the facilities for investigation afforded by his 
laboratory at Newport, R. 1. 
T Although this is certainly the last stage of the zo&a (I obtained the young erab 
from it after a single cast of the skin), the mandibular palpus is not developed to 
anything like the extent seen in Dohrn’s figure of a Porcellana zoéa,  (Untersu- 
chungen über Bau und Entwicklung der Arthropoden.  Zeits. Wiss. Zool. XXI. 
p. 373; Taf. XXIX. Fig. 51. 1871. Claus, describing a Porcellana zoéa from 
Nice in a stage corresponding to the one before us (Marburger Sitzungsberichte, 
1867, p. 15), states that the mandibles are destitute of palpi; but in his later work, 
“Untersuchungen zur Erforsehung der Genealogischen Grundlage des Crustaceen- 
Systems," 1876 (p. 58), describing the same stage, he says the rudiment of the palpus 
exists as a simple prominence, 
