158 BULLETIlJT 93, UNITED STATES NATIONAL MUSEUM. 



In a specimen growing on an oyster, taken at Fish Ilaioh station 

 1595, Long Island Sound, 1890, the scutum has the adductor ridge 

 almost as well developed as in the Pacific B. rostrcdus. The external 

 characters and tergum are as in typical B. halamis. The diameter 

 of the base is about 21 mm. 



On the coasts of Nova Scotia and Maine, and the fishing banks off- 

 shore, we find, together with subtypical B. halanus, a large, very 

 strongly ribbed, thick-walled form, which Conrad called B. genicu- 

 latus. It has the same rib arrangement as the Belfast form, costatus, 

 but the aspect is different; size larger, ribs high and angular, in- 

 tervals wide, concave. Conrad's tjq^e-specimen is figured (pi. 34, 

 fig. 3), No. 2105 A.N.S.P. A group of smaller, higher specimens 

 from the Bay of Fundy, growing on a smooth stone, is shown in 

 plate 31, figure 7, Cat. No. 2303 U.S.N.M. The size is often con- 

 siderable. Carinorostral diameter, 41 nun. ; lateral diameter, 42 mm. ; 

 height, 30 mm. (Eastport). Carinorostral diameter, 50 mm.; lateral 

 diameter, 39 mm.; height, 32 mm. (Georges Bank). 



The very strongly ribbed form from the Bay of Fundy (pi. 34, 

 fig. 7) has cirri differing in several respects from British examples. 

 The sixth cirrus has 49 segments, which are decidedly shorter than 

 usual, and bear six pairs of spines (fig. 43^). Penis short, as 

 usual. As in all Afnerican specimens examined, the cirri are light 

 yelloio, not dark as described by Darwin. The mandible is figured 

 (fig. 43^). 



Long Island Sound is the extreme southwestern point for B. hala- 

 7ms on our coast. Offshore it reaches a little farther south. Latitude 

 40° 13' 15" north, near the southern edge of the continental shelf, 

 in about the latitude of Asbury Park, New Jersey, but farther east 

 tlian Nantucket, is the extreme southern range known for B. halanus 

 in the western Atlantic. The total range in latitude is therefore 

 slightly over 40 degrees. 



The temperatures recorded are mainly between 40° and 55° F., 

 but at one station in Vineyard Sound, 69° F. (Aug. 27, 1887). ^ 



A remarkable peculiarity in the distribution of B. halanus is its 

 absence from the Great Banks of Newfoundland, where the com- 

 panion species B. crenatus is abundant. 



Alaska and Bering Sea. — B. halanus is known from latitude 57^ 

 18' north to the Aleutian Islands, and a form occurs in Puget Sound, 

 widely separated from the northern herd, probably because we have 

 few near-shore collections from intermediate points. 



There is no feature of the hard parts differentiating Bering 

 Sea specimens from some of those of the western Atlantic, but 



1 At 18 fathoms in Vineyard Sound there is a difference of at least 22° F. between the winter and summer 

 bottom temperature at one station. See Sumner, Biological Survey of Woods Hole and Vicinity (Bull. 

 Bur. of Fisheries, vol. 31, 1911). 



