162 PROCEEDINGS OF THE NATIONAL MUSEUM vol. loi 



byssal threads and thus encased with the seaweed and byssal threads 

 lays a string of eggs that develop into young clams within the seaweed- 

 byssal "nest." At Point Barrow there are no seaweeds that could 

 be used in this manner and the animal makes its capsule entirely of 

 byssal threads. I examined 3 specimens of var. laevigatus from the 

 northeast end of the Melville Peninsula and 3 from the south end 

 that were in byssal nests with pieces of C/Zw-like alga attached. 



The Pacific specimens of varieties of M. discors usually have been 

 listed under the specific names of Modiolaria laevigata and M. suh- 

 striata by Western authors. 



Distribution: Varieties of M. discors are found throughout the 

 Arctic and as far south as Japan and Puget Sound in the Pacific and 

 New York and Madeira in the Atlantic. As at Point Barrow, the 

 var. laevigatus is more common in both eastern and western Greenland 

 and in Iceland than the forma substraitus (Jensen, 1912; Madsen, 

 1949). 



Order Anomalodesmacea 



Family Thraciidae 



Genus Thracia Blainville, 1824 



Thracia myopsis (Moller, 1842, ex Beck MS.) 



Plate 23, figure 9; Plate 24, figure 4 



Thracia myopsis Moller, 1842a, p. 18; 1842b, p. 94.— Soot-Ryen, 1941, p. 38' 



pi. 2, figs. 1-4; pi. 6, figs. 3a-b; pi. 8, figs. 4a-e. 

 Thracia curta Dall, 1921, p. 25 (in part) .— Oldroyd, 1924, p. 84 (in part). 



One right valve 30.5 mm. long and 24.3 mm. high was taken at 217 

 feet, and 1 entire (only recently vacated) shell 30 mm. long and 22.5 

 mm. high was taken at 341 feet. 



Other material examined: A number of specimens from Icy 

 Cape, Cape Sabine, Plover Bay, off Bristol Bay, Amchitka Island, 

 Atka Island, and Port Etches (all of which were labeled T. curta). 

 Also several specimens (labeled T. myopsis) from Bergen and Vads0, 

 Norway, from Spitzbergen, and from Greenland and Maine. 



Discussion: The Point Barrow specimens correspond with those 

 examined from Bergen and Vads0. Those from Greenland and Spitz- 

 bergen are a trifle more elongate, a trifle more angular, and somewhat 

 more abruptly truncate. The specimens from Maine are somewhat 

 higher and more truncate and have a somewhat shorter posterior end. 



In examining specimens of Thracia, it was found that those from 

 Port Etches and northward are T. myopsis and those from Lituya Bay 

 and Sitka and on south are T. curta Conrad. The northernmost range 

 of T. curta thus becomes Lituya Bay (about lat. 58.5° N. instead of 

 lat. 71° N.). In T. curta the beaks are more posteriorly placed and 



