INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 239 



quite different from the adult. The carapax is about 3 rnin long and 

 slightly less in breadth. The front is much more promim-nt 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 antenna3 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 zoe'a 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 zoea 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 

 irroratus, and resembles it much in general appearance, but the carapax 

 is much broader in proportion, the rostrum is a little longer, and there 

 is a marked 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 sctce 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 03 55' east, Septem- 

 ber 14. It would fall in the genus Cyllene of Dana, and is closely allied 

 to his Cyllene furciger (Crust. U. S. Expl. Expd., p. 494, Plate XXXI, 

 fig. 8) from the Sooloo Sea. In one specimen the carapax, including 

 the rostrum, is 2.0 mm long, excluding rostrum, 1.6 mm , breadth, l.l mm . 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 



