40 RECENT BIVALVE MOLLUSKS 



Gciius Spisula Gray, 1838. 



Subgenus Hemimactra Swainson, 1840. 



Section ]\Iactronieris Conrad, 1868. 



Hemimactra polynyma Stm., var. alaskana Dall, 1894. 



Arctic Ocean at Cape Lisbnrne, south to Bering Sea and 

 the Aleutians and eastward to Puget Sound. North 

 Japan, the Kurile Islands and the Okhotsk Sea (Schrenck). 



Hemimactra hemphilli Dall, 1894. 

 San Pedro to San Diego, Cal. 



Hemimactra catilliformis Conrad, 1867. 

 Neeah Bay to San Diego, Cal. 



Hemimactra falcata Gould, 1850. 



Puget Sound to Cortez Bank and the Coronado Islands. 



Subgenus Symmorphomactra, Dall, 1894. 



Symmorphomactra planulata Conrad. 1837. 

 Monterey to' Cape St. Lucas. 



Genus Schizoth?erus Conrad, 1853. 



Schizothaerus nuttallii Conrad, 1837. 



AVrangell, Alaska, to San Diego. Cal. 

 Schizothaerus nuttallii var. capax Gould, 1850. 



Kadiak Island. Alaska, to San Francisco, Cal. 



Family Mesodesmatidse 

 Genus Ervilia Turton. 1822. 



Ervilia californica Dall. 1916. 



San Pedro. Cal., to San Diego. 



Superfamily Myacea 



Family Myacidae 



Genus ]\Iya (L.) Lamarck, 1799. 



Mya truncata Linne, 1758. 



Circumboreal. Arctic Ocean to Bering Island on the 

 west and to Puget Sound on the east. 



Mya intermedia Dall. 1898. 



Arctic Ocean from Point Barrow to ]Monterey Bay, Cal. 



Mya arenaria Linne, 1758. 



Mctoria. B. C, to Monterey, Cal. Introduced at San Fran- 

 cisco with '"seed" oysters from the Atlantic coast. 



Genus Cryptomya Conrad, 1849. 



Cryptomya californica Conrad, 1837. 



Chichagoff Island. Alaska, and south to Topolobampo, 

 Mexico. 



