138 BUUvETIN OF THE BUREAU OF FISHERIES. 



Most of the decapods collected by us, being of large size and having rather obvious 

 specific distinctions, were listed with full confidence in the field. The others were, for 

 the most part, referred to Miss M. J. Rathbun, to whom we are likewise indebted for 

 criticizing our check-list of local decapods and for information generously given through- 

 out the progress of this work. To Dr. R. P. Bigelow we are indebted for the identifica- 

 tion of a number of specimens collected during the first season of the dredging work. 



Errors due to the confusion of one species with another in our dredging records are 

 probably negligible in extent, excepting, perhaps, such as may relate to the small crabs 

 of Panopeus group (now split into several genera). Upon this point the reader is 

 referred to the statements made under the head of Eurypanopeus depressus, Neopanope 

 texana sayi, and Hexapanopeus angustijrons in the annotated list. It seems possible 

 that specimens identified by the collectors as "Panopeus sayi" were in some cases 

 referable to one of the other species. It is probable, however, that the great majority 

 of these crabs actually belong to the species last named, since none of the others are 

 comparable with it in respect to frequency of occurrence. The examination of a 

 large number of our specimens by Miss Rathbun indicates that Eurypanopeus depressus 

 is at present comparatively rare in these waters, being by no means the common species 

 which one would infer it to be from the statements of Smith. 



The average number of species of decapods recorded by us from the 458 regular 

 stations of the Survey is 3.5 per dredge haul. By far the most prevalent single species 

 was Pagurus longicarpus, which was recorded from 290, or over 60 per cent, of the 

 stations. Those species which were dredged at one-fourth or more of the total number 

 of stations (arranged in order of frequency) are: 



Number of stations. 



Pagurus longicarpus 290 



Cancer irroratus 209 



Pagurus annulipes 196 



Libinia emarginata 192 



Crago septemspinosus 169 



Neopanope texana sayi 143 



For the various groups of dredging stations and for the various types of bottom 

 the averages are surprisingly uniform. The following figures are taken from the tables 

 on pages 78 and 79: 



Vineyard Sound: 



Fish Hawk 3. 8 



Phalarope 3. 2 



Buzzards Bay: 



Fish Hawk 3. 4 



Phalarope 3. 2 



Type of bottom : 



Sand 3. 5 



Stones and gravel 3. 5 



Mud 3.6 



The lists of "prevalent" species for these different groups of stations are likewise 

 surprisingly uniform in respect to the species comprised. Of the 6 species listed for 

 one-fourth or more of the total number of stations, 3 appear in all seven of the lists 

 of "prevalent" species; 2 others appear in all but one of these lists, while the remaining 

 species appears in five of the seven lists. The lists of "prevalent" species for the three 

 types of bottom comprise 5 species each. Of these, 4 are common to all three lists. 



