252 bulletin: museum of comparative zoology. 



stage is well known (A. Agassiz, 1865), is Melicertum campanula; 

 a jelly-fish swarming in the bays and among the islands of the Gulf 

 (1914a, p. 25). But in all our cruises we have only once found Meli- 

 certum more than fifteen miles from land, a single specimen in the 

 Western Basin, in August, 1913 (Station 10088). The medusae of the 

 genus Sarsia are similarly restricted to the coast, for while they are 

 liberated in great numbers along shore, and on the shallow coastal 

 banks in spring (1914b, p. 407) we have never taken any in the central 

 parts of the Gulf, and only rarely more than a few miles from land. 



Still another example of neritic occurrence is afforded by the hydroid 

 colonies which float, in swarms, over Nantucket Shoals (1915, p. 306) 

 and Georges Bank (1914b, p. 414) early in the season, but which are 

 so closely confined to the regions where they are torn from the bottom, 

 . that we have never found them nor their free medusae, anywhere in the 

 deep central parts of the Gulf. 



There are, it is true, several medusae, with fixed stage, which do 

 occur more or less generally over the Gulf, for example Staurophora 

 N^ and to a less degree PhiaUdium languidum (1914a). But this is to be 



explained on the assumption that their fixed stage is not confined to 

 shallow water. They are thus in the same class as Sebastes, among 

 fishes (p. 280) so far as their dispersal over the Gulf is concerned. 



Among the Crustacea excellent examples of the neritic habit are 

 afforded by the pelagic larval stages of the various littoral decapods, 

 particularly the crabs; and by the phyllopod genus Evadne (Gran, 

 1902). 



Young crabs (Cancer sp.) are produced in large numbers all along 

 the coast line, in July; and they are usually represeiited in the summer 

 hauls near land, occasionally in swarms, for example, in Ipswich Bay, 

 and off Rye, on July 23, 1915. But they have never been detected 

 in our offshore hauls; and what is true of crab larvae holds equally 

 for the other metozoan larvae which are so important a part of the 

 plankton near shore. Evadne, long recognized as one of the most 

 important index forms of the plankton (Gran, 1902; Apstein, 1910; 

 Herdman and Riddel, 1911), occurs regularly in summer in the Bay 

 of Fundy off the mouth of the St. Croix river (Willey, 1913), as well as 

 off the Nova Scotian coast (Wright, 1907). But in 1915 we detected 

 it at only nine Stations (10287, 10302, 10303, 10313, 10317, 10318, 

 10319 and in Shelburne Harbor), all within ten miles of land, and 

 most of them much nearer; and although Evadne is a seasonal or- 

 ganism, its absence in the more oceanic parts of the Gulf can hardly 

 be laid to the season because the offshore work continued from spring 

 to autumn. 



