MUSEUM OF COMPARATIVE ZOOLOGY, 265 
from the zoéa to the crab in the species described in this paper, and that he 
had, besides, another zoéa, apparently distinguished from mine only by its 
slightly smaller size and shorter spines, which passed into a megalopa phase ! 
In this stage (a tracing of which is enclosed in Professor Smith’s letter) the 
carapace is broad and crab-like, without a vestige of the spines of the zoéa, 
This megalopa subsequently changed into a young crab very nearly like that 
which developed immediately from the long-spined zoéa.* 
It would seem, therefore, that two species of Pinmixa occur, at least in the 
young stages, on the southern shore of New England, which present a remark- 
able difference in their development. While the one goes through the custom- 
ary megalopa condition, the other passes, by a syncopated development, from 
the zoéa directly into the brachyurous state. 
CAMBRIDGE, January, 1879. 
EXPLANATION OF THE PLATES. 
Nors. I am greatly indebted to my brother, Mr. Charles E. Faxon, for preparing my drawings 
for the heliotypie process. 
PLATE I Hippa talpoida. 
Fig. 1. Cluster of segmented eggs taken from the abdominal appendages of a fe- 
male. "The eggs are spherical, about 1,5 mm. in diameter, of a bright 
orange-yellow color. 
Fig. 2. Egg with the enclosed embryo in the ‘nauplius-stage” : a, labrum ; b, 
antenna of the first pair ; c, antenna of the second pair ; d, mandible ; 
e, abdomen ; f, yelk. 
Fig. 3. Embryo further advanced: a, rostrum ; 6, cephalic plate; c, antenna of 
first pair; d, antenna of second pair ; e, mandible ; f, first maxilla ; g, 
second maxilla ; /, first maxilliped ; 4, second maxilliped (even at this 
early stage, the appendages back of the mandible are double) ; و‎ abdo- 
men (the likeness of the abdomen in this embryonic stage to the abdomen 
of prawn-zo& is suggestive). 
Fig. 4. The same, from a different point of view : a, antenna of first pair; b, an- 
tenna of second pair; ¢, mandible ; d, first maxilla ; e, second maxilla ; 
J, first maxilliped ; y, second maxilliped ; 4, hind border of carapace, 
* Professor Smith has also kindly sent me tracings of the zova of Pinnotheres 
maculatus raised from eggs. It has a long dorsal spine (wholly wanting in Thomp- 
son's figures of the zoëa of Pinnotheres pisum), and the abdomen is like that figured 
by Fritz Müller as Pinnotheres, “Für Darwin," Fig. 19 ) supra, p. 263, note}. Al- 
together the zoëa bears less resemblance to the zoéa of Pinnotheres pisum, as represented 
by Thompson, than the zoóa of Pinnixa does! It should be noted that the accuracy 
of Thompson’s figures is attested by Bell (** British Stalk-eyed Crustacea,” p. 125). 
