Crustacea on the coast of New England. 261 



America agree well with Stimpson's description of P. socius in want- 

 ing the patch of dark color usnally present at the bases of the pio- 

 podal digits of the chelipeds of Atlantic Ocean specimens ; but in a 

 large series of Atlantic specimens before me there is very great 

 variation in the extent and intensity of the color upon the chelipeds 

 and other parts of the animal, and some of the specimens from 

 Bermuda, and one of those from Brazil want wholly the dark spot 

 upon the chelipeds. The only other characters Stimpson points out 

 for distinguishing the socius are : " the carapax is somewhat nar- 

 rower, less convex, and more strongly striated; and the frontal 

 region is more depressed and expanded." The impossibility of dis- 

 tinguishing Pacific sj^ecimens by the narrowness of the carapax or 

 breadth of the front is fully shown in the table of measurements 

 beyond. The convexity and striation of the carapax vary consider- 

 ably in Atlantic specimens, and in those examined more than enough 

 to include all the Pacific specimens seen. 



Several of the specimens from Bermuda have the branchial regions 

 of the carapax much more convex and swollen than is usual, and the 

 convexity is not always equal on the two sides of the carapax. In 

 at least a part of these specimens this irregularity in the form of the 

 branchial region is due to the presence of a Bopyroid parasite within 

 the branchial cavity, and I think it very probable that Saussure's 

 mineatus was based on similar parasited specimens. 



Heller compares his intermedius Avith Dana's innotatus and simplex 

 and says that innotatus differs from his species only in having the 

 carpus, as well as the hand, smooth above. Heller had apparently 

 seen no specimens of innotatus., which is described as having the 

 carpus " smooth" above (although the figure shows indication of 

 slight corrugation), and depended on this one supposed difference for 

 distinguishing the species. There is, as might be expected, con- 

 siderable variation in the amount of corrugation upon the carpus, 

 some specimens having the carpus very nearly or quite smooth to 

 the naked eye, though in specimens of considerable size it is usually 

 very distinctly corrugated, and I have no doubt Heller would have 

 identified his specimens with the innotatus had he had Dana's speci- 

 mens for comparison. There is certainly nothing in Heller's descrip- 

 tion to distinguish his species from ordinary specimens of transversus 

 from Bermuda and Florida. 



The following measurements of the carapax in a large number of 

 specimens were made with special reference to determining the difler- 

 ence in proportions between Atlantic and Pacific specimens. In 



