438 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



carapax is considerably more slender than in P. Monfagiii, and tlie pos- 

 terior tooth of the dorsal carina is farther forward, being: much in front 

 of tlie middle. The abdomen is more slender than in P. Montagui; but, 

 except for the greater slenderness, there is scarcely any difference in 

 the form or jjroportions of the somites, or the form and armature of the 

 telson and nropods. There are slender exopods, about a third as long 

 as the ischia, at the bases of the external maxillipeds, but the endopods 

 themselves are as in P. Montagui; the merus reaches to the base of the 

 flagellum of the antenna, and the tip falls considerably short of the tip 

 of the antenna! scale. 



The first pair of legs are nearly as in P. Montagui. The right chelate 

 leg of the second pair is shorter and stouter than in P. Montagui^ and 

 scarcely reaches the tip of the corresponding leg of the first pair ; the 

 ischium is about a fourth the entire length ; the merus is only a little 

 shorter than the ischium ; the carpus increases in thickness distally, is 

 a little longer than the ischium, not more than about once and a half as 

 long as the merus, and usually composed of only five segments, the 

 jnoximal half being wholly unsegmented or annulated, then three sub- 

 equal and very distinct segments, about as broad as long, and these fol- 

 lowed by the terminal segment, which is about as long as the three next 

 l^receding; the chela is about half as long as the carpus and a little 

 stouter than its distal end.* The left chelate leg is a little shorter and 

 stouter than in P. Montagui^ but has about the same number of seg- 

 ments in the merus and carpus, and does not differ in other respects. 

 The third, fourth, and fifth pairs of legs differ from tbose of P. 3fontagi(i 

 in being a little more slender and in having much longer, much more 

 slender, and nearly cylindrical dactyli, which are wholly unarmed, except 

 a few small spinules beneath near the base. 



* The proportions of tho segments and the segmentation of the carpus in the nn- 

 equal second pair of legs in the genus Pandalus appear to he usually very constant and 

 to afford very good specific characters, hut they occasionally present very remarkahle 

 variations. In carefully examining several hundred specimens of this species, onlj^ 

 about half a dozen were found which varied from the above description in the seg- 

 mentation of the left carpus ; two or three specimens had an additional hut less dis- 

 tinctly indicated segment back of^the four distal ones, making six in all. Two speci- 

 mens had three additional segments inserted in the same way, making eight in all; 

 l»nt in both these specimens the segmentation was more or less irregular, and the addi- 

 tional segments may have resulted from some injury. One large female, quite normal 

 in other respects, has the right carpus multiarticulate throughout and composed of 

 about eighteen segments, nearly as in P. Montar/ui; the whole leg, however, is shorter 

 than in other specimens of the same size, and may have been reproduced, though I 

 cannot see how this would explain its abnormal structure. Detailed measurements 

 of both chelate legs in most of the^ abnormal specimens are given beyond in the tables 

 of measurements. 



One female, 70'"'" long, stations 290 to 291, 30 to 31 fathoms, off Cape Cod, has the 

 chelate legs reversed, just as in the specimen of P. projnnquus already referred to. 



