114 



BULLETIN OF THE BUREAU OF FISHERIES. 



and in the great majority of cases (72 per cent) it was taken at depths greater than 10 

 fathoms." 



Comparing the range of these two species upon our coast, we find that Arbacia is 

 said to occur from "Nantucket Shoals and Woods Hole to west Florida and Yucatan" 

 (Clark), i. e., our region lies at its northern limit of distribution. The range of Sirongy- 

 locentroius, on the other hand, is said to be "circumpolar; southward in the western 

 Atlantic to New Jersey (not in shallow water south of Cape Cod)." 



That Arbacia is not adapted to enduring temperatures lower than those generally 

 prevailing in our local waters during the winter months is indicated by the fact that a 

 large proportion of these urchins seem to have been exterminated in Vineyard Sound 

 during the winter of 1903-4. This winter was an extremely severe one, the ice being 

 greater in quantity and lasting longer than for many years previously. Even Woods 

 Hole passage, where the tidal currents are extremely swift, was frozen over so firmly 

 that Mr. Vinal Edwards accomplished the astonishing feat of walking over to Nona- 

 messet Island. Reference to the temperature tables for the Woods Hole station (p. 47) 

 shows that the mean water temperature for January and February, 1904, was 29.3° F., 

 as compared with 32.3°, the mean of these two months for the other four years comprised 

 in the table. 



Now the sudden and extreme scarcity of Arbacia in Woods Hole Harbor and else- 

 where in the summer of 1904 was noted by local collectors generally, and we are informed 

 by the curator of the Marine Biological Laboratory, Mr. George M. Gray, that this 

 species did not for several years resume anything like its former abundance in local 

 waters.* 



Fortunately we are in possession of definite data on this subject, based upon a 

 comparison of our dredging records for the summers of 1903 and 1904. As has been 

 stated on page 55, a considerable number of the 1903 stations were repeated in the 

 following summer for the sake of comparisons and verifications. In the two parallel 

 columns below we present the records for Arbaciu, obtained during these two seasons, 

 in that part of the Sound (the eastern two-thirds) in which the stations were duphcated: 



I903- 



7522 (many living). 



7523 (several living). 



7524 (very abundant, living). 

 7S26'(2). 



7529 (few). 



7530 (abundant). 



7531 (i dead). 



7532 (many). 



7533 (few, many spines). 



7534 (numerous). 



7535 (few shells, many spines). 



7537 (many, rather small). 



7539 (few). 



7540 (few). 



1904. 

 752 ibis (fragments and spines). 

 7522bis (none). 

 7S23bis(i spine). 

 7524bis (none). 



753obis (none). 



753 ibis (few fragments). 



7532bis (few spines). 



7533bis (i small living). 



7534bis (few spines). 



7S35bis (many spines). 



7536bis (many spines). 



7537bis (none). 



7538bis (spines and fragments). 



7S39bis (none). 



o This despite the fact that hardly more than a third of our stations were in waters as deep as that. 



* In 1908 and 1909 we were able to obtain large quantities of these urchins in Vineyard Sound by means of tangles. 



