364 
BULLETIN OF THE BUREAU OF FISHERIES 
it has been found as far north as Y, where the salinity at the bottom is often not more 
than 16.00 to 17.00 per mille. Nearly all of the 29 specimens constituting the Chesa- 
peake collection in the National Museum are juvenile forms, as in the case of L. 
marginata. No ovigerous specimens were collected. The records show that speci- 
mens of L. dubia have been found in the bay at all seasons of the year. We have 
temperature records taken near the bottom for the areas at which this form was 
collected. They range from 7.9° C. to 24.4° C. 
Finally, there is the spider crab, Pelia mutica (Gibbes), which has been collected 
along the Eastern Shore in Tangier Sound and a few other localities. Specimens of 
this form were collected by U. S. S. Fish Hawk in June, 1891, but none has been 
taken on the Chesapeake survey cruises during 1915, 1916, 1920, 1921, and 1922. 
It should be mentioned, however, that Tangier Sound was not visited at regular 
intervals during these cruises. P. mutica is known to frequent bays and sounds. 
(Rathbun, 1925, p. 279.) 
It is clear that some of the Crustacea collected from Chesapeake Bay and vicinity 
have been found exclusively outside of the bay, where the salinity is high, that some 
have been found exclusively in the bay, where the salinity is much lower. But our 
data show that others occur in both regions, even though the range of salinities is very 
great. Furthermore, there is good reason for believing that some Crustacea migrate 
from one end of the bay to the other at certain times of the year. So it seems prob- 
able that some Crustacea can survive a great range of salinities, at least if the changes 
take place gradually. Fredericq (1898, p. 831) has been able to increase or diminish 
to a large extent the salts in the blood of the crab, Carcinus maenas, by placing the 
specimen successively in water of greater or less salinity. Also, he (1889) finds that 
the blood of C. maenas varies with the degree of salinity of the water in which the 
animal is living. The investigations of other workers such as Issel on copepods, 
Herdman on copepods, Schmankewitsch on Artemia salina (see Flattely and Walton, 
1922), and Loeb (1903) on Gammarus show that these forms are able to stand a wide 
range of salinities. More recently Adolph (1925) has found that a marine species of 
Gammarus "will live indefinitely if transferred to sea water diluted with distilled 
water up to 0.5 per cent (0.005 M), or concentrated by the addition of salts up to 
160 per cent (1.56 M, corrected for ionization).” 
Why some forms have been found only in the lower part of the bay or outside, 
or in both regions and not in the upper part of the bay, are questions which can not 
be answered without a careful study of the habits and physiology of individuals of 
each species in as many of the environments to which they may be subjected in nature. 
ARACHNOIDEA 
The Xiphosura or horseshoe crabs are represented in Chesapeake Bay by one 
species, the common Limulus polyphemus (L), which was taken in the beam trawl 
on several occasions. It was found in September, 1916, at area A; in January and 
December, 1920, at 6 and in May, 1920, at F and E. Only eight specimens were 
captured, all of which, as may be seen from the areas listed, came from near the mouth 
of the bay. The bottom salinities and temperatures for these areas (area G' during 
the December cruise excepted) ranged from 22.60 to 29.22 per mille and from 2.7° C. 
to 23.4° C., respectively. The records indicate that L. polyphemus may be found 
throughout the year in the bay, but only in its lowermost portion. 
At least one species of the order Pycnogonida has been found by us in Chesapeake 
Bay. It has been identified, tentatively, by the United States National Museum 
