[533] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 239 
quite different from the adult. The carapax is about 3" long and 
slightly less in breadth. The front is much more prominent than in 
the adult, but still has the same number of lobes and the same general 
form. The antero-lateral margin is much more longitudinal than in the 
adult, and is armed with the five normal teeth, which are long and 
acute, and four very much smaller secondary teeth alternating with 
the normal ones. The antenne and ambulatory legs are proportionally 
longer than in the adult. The young crabs in this stage were once or 
twice taken in the towing-net, but they were not common at the surface, 
although a large number were found, with a few in the megalops stage, 
among hydroids upon a floating barrel in Vineyard Sound, July 7. 
The young of Platyonichus ocellatus in the zoéa and megalops stages 
were frequently taken in the towing-net from the last of June till August, 
but they were much less abundant than the young of Cancer irroratus. 
On June 29, however, they occurred in great numbers. Twenty-two 
out of forty of those in the zoéa state changed to the megalops during 
the first twenty-four hours, and in the same time ten out of fifty in the 
megalops stage changed to the adult form, so that they probably do not 
remain in the megalops state longer than the young of Cancer irroratus. 
They apparently do not molt during the megalops stage. 
The megalops of the Platyonichus is about the size of that of Cancer 
ivroratus, and resembles it much in general appearance, but the carapax 
is much broader in proportion, the rostrum is a little longer, and there 
is amarked prominence at the anterior margin of the orbit, representing 
the lateral tooth of the front of the adult, and a similar prominence, rep- 
resenting the stout postorbital tooth, at the posterior angle of the orbit. 
The spine upon the cardiac region is rather more slender than in the 
megalops of the Cancer. The chelipeds are more elongated, and much 
like those of the adult Platyonichus, except that they want the stout 
spines of the latter. The dactyli of the posterior legs already approach 
in form those of the adult, being expanded into narrow oval plates a 
fourth as broad as long. The tips of each of these dactyli are furnished 
with four peculiar set of different lengths and with strongly curved ex- 
tremities, the longest and two shortest of which are simple, while next 
to the longest one is furnished along the inner side of the curved extrem- 
ity with little, closely set, sack-like appendages. 
Another megalops, belonging apparently to some swimming-crab, was 
several times taken in the towing-net, in Vineyard Sound, from August 
11 to September 3, and was also taken by Mr. Harger and myself, east 
of George’s Bank, latitude 41° 25/ north, longitude 63° 55/ east, Septem- 
ber 14. It would fall in the genus Cyllene of Dana, and is closely allied 
to his Cyllene furciger (Crust. U. 8S. Expl. Expd., p. 494, Plate XX XI, 
fig. 8) from the Sooloo Sea. In one specimen the carapax, including 
the rostrum, is 2.0"™ long, excluding rostrum, 1.6"", breadth, 1.1™". The 
front is quite narrow between the bases of the ocular peduncles, and 
has a long and slender rostrum. There are no prominences either side 
