INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 525 



lation at the base, and three seta? at the tip. The antenna? have large 

 well developed scales, furnished along the inner margin with long 

 plumose hairs, but the nagelluni is shorter than the scale, not divided 

 into segments, and has three plumose seta? at tip. The mandibles are 

 unlike on the two sides ; the inferior edges are armed with acute teeth, 

 except at the posterior angle, where there is a small molar area ; the palpi 

 are very small, with the three segments just indicated. The exognathus 

 in both pairs of maxillae is composed of only one article, and is furnished 

 with several seta? at tip. In the first maxillipeds the exognathus is an 

 unarticulated process, furnished with short plumose hairs on the outer 

 side. The second maxillipeds have the principal branch cylindrical, 

 .not flattened and appressed to the inner mouth organs as iu the adult; 

 the exognathus is short, and as yet scarcely flabelliforin ; and the epig. 

 nathus is a simple process, with not even the rudiment of a branchia. 

 The external maxillipeds are pediform, the endognathus as long as and 

 much resembling the endopodi of the posterior legs, while the exog- 

 nathus is like the exopodi of all the legs, being half as long as the en- 

 dognathus, and the terminal portion furnished along the edges with long 

 plumose hairs. The epignathus and the branchia? are very rudimentary, 

 represented by minute sack-like processes. . The anterior cephalothoracic 

 legs, (Fig. D,) which in the adult develop into the big claws, are exactly 

 alike, and no longer than the external maxillipeds. The pediform branch 

 is, however, somewhat stouter than in the other legs, aud subcheliform. 

 The legs of the second and third pairs are similar to the first, but not 

 as stout. The legs of the fourth and fifth pairs are still more slender, 

 and stjdiform at the extremity, as in the adult. 



The exopodal branches of all the legs and of the external maxillipeds 

 are quite similar, and differ very little in size. In life, while the animal is 

 poised at rest in the water, they are carried horizontally, as represented in 

 Figure B, or are curved up over the carapax, sometimes so as almost to 

 cover it. The blood circulates rapidly in these appendages, and they 

 undoubtedly serve, to a certain extent, as respiratory organs, as well as 

 for locomotion. By careful examination, small processes were found 

 representing the normal number of branchia? to each leg.* These rudi- 

 mentary branchia?, however, differ somewhat in different specimens, 

 being very small, and scarcely distinguishable, in what appear to be 

 younger individuals, from the rudimentary epipodi, whije in others, ap- 

 X)arently older, they are further developed, being larger, more cellular in 

 structure than the epipodi, and even showing an approach to crenulation 

 in the margins, as shown in Figure D. 



The abdomen is slender, the second to the fifth segments each armed 

 with a large dorsal spine, curved backward, and with the lateral angles 



* The number of brauchire, or branchial pyramids, iu the American lobster is twenty 

 on each side; a single small one upon the second maxilliped, three well developed ones 

 upon the external maxilliped, three upon the first cephalothoracic leg, four each upon 

 the second, third, aud fourth, and oue upon the fifth. 



