306 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
occasionally appear there both in summer (1914a) and-in winter 
(1914b). 
The demarcation between the ranges of Limacina balea and of the 
warm water pteropods and heteropods, 2. e., the various species of | 
Creseis, Corolla, Limacina inflata, Pterotrachea, Firoloida, and Atlanta, 
was remarkably sharp, for the latter were only taken at the southern 
and Gulf Stream stations where Limacina balea was lacking (Fig. 72); 
and not a specimen of any of them was found at any of the northern 
stations where Limacina balea occurred, except for a single Atlanta 
off Gloucester. They are all oceanic, as pointed out by Meisenheimer 
(1905). None of them occurred regularly, only one (Creseis conica) at 
as many as five of the eighteen stations south of the limits of Liamacina 
balea; and the total number of specimens of this species was only 
forty-nine. ‘The other warm water forms were even more sporadic in 
their distribution :— Corolla calceola, Firoloida, and Creseis acicula oc- 
curring at four stations each; the others at only one or two. Under 
these circumstances it is impossible to say much about the influence 
of hydrographic conditions on their distribution further than to point 
out that all have a southern, or oceanic origin, and that it is doubtful 
whether any of them would have been found in the coast water im 
winter. Direct evidence to the effect that they are summer visitors 
only is afforded by the fact that none of them were taken by Capt. 
McFarland off Cape May in May, 1913, although several were en- 
countered there in July. 
The occurrence of two living specimens of Diacria trispinosa, and 
of an Atlanta, in a haul off Gloucester early in July is surprising, 
because it is certain that neither of these genera is a regular inhabitant 
of the Gulf of Maine; both belong to the warmer parts of the north 
Atlantic, not to boreal waters (Meisenheimer, 1905). It is difficult to 
account for their presence, because they were taken with an otherwise 
typical boreal assemblage of plankton organisms, e. g., Calanus, Euthe- 
misto. 
PELAGIC HYDROIDS. 
BY C. MCLEAN FRASER. 
During the month of July, 1913, the Grampus made a collection of 
floating hydroids off George’s Bank, which, through the kindness of 
Dr. H. B. Bigelow, was sent to me for examination. Under ordinary 
circumstances the material would scarcely be worth a comment as 
