DECAPODS 5 



abundant species are Pandalus borcalis and P. montagui, both 

 boreal forms which descend from the Arctic regions into the At- 

 lantic as well as the Pacific, but in the latter find conditions most 

 favorable to their increase. The form of P. montagui inhabiting 

 the Pacific exhibits modifications which entitle it to recognition 

 as a distinct subspecies. 



In number of species the genus Spirontocaris of the family 

 Hippolytidae is unsurpassed. Like Pandalus, it is primarily a 

 boreal genus, and is common to the Atlantic and the Pacific. In 

 the Pacific it is represented by 5 I species, exhibiting great diver- 

 sity in form. Several are identical with Atlantic species. 



Quite as conspicuous in the North Pacific fauna are the Cran- 

 gonidas. These occur in great numbers, and exhibit 32 different 

 forms, for the most part restricted to the Pacific. 



The Paguridse, or hermit-crabs, occur in vast numbers, and some 

 of the species appear to have local centers of distribution. Each 

 of these species attains its maximum development, both as to size 

 and numbers, in a particular area, while elsewhere it is stunted 

 and infrequent. 



Several of the spider-crabs (Maiidae) abound in shallow as well 

 as in deeper water, and Oregonia, CJiorilia, the two Chionoecetes, 

 and the two species of Hyas form no inconsiderable part of every 

 haul of the dredge. 



Less abundant are the Lithodidas or Anomuran spider-crabs, 

 which include the giant Decapods of the region. 



The crowding of crustacean life in certain localities is especially 

 favorable to parasitism. Bopyrids (of a few species only) are of 

 frequent occurrence on many species of shrimps 1 ; Rhizocephalids 

 are less common, while worm parasites have been noticed in sev- 

 eral instances embedded underneath the carapace of Spirontocaris. 



The Decapods contribute without doubt a large proportion of 

 the food of fishes, several species having been taken from their 

 stomachs ; but our knowledge on this subject is very fragmentary. 



Many species are caught for the market, to be used for the 

 table or for bait. The list of these furnished in ' The Fisheries 

 and Fishery Industries of the United States,' Washington, 1884, 



1 Miss Harriet Richardson will publish a report on the Bopyridae of the Museum 

 collection in the Proceedings of the U. S. National Museum during the next year. 



