NO. 1906. A ZOOOEOORAPHIC STUDY— BART SCH. 299 



region between Chiloe Island and the Strait of Magellan, the other, 

 the Antarctic, in the restricted sense, corresponding to the Arctic, 

 in the restricted sense, of the northern hemisphere, covering the 

 South Shetlands and tlie territory to the south of them. 



The present study is the first actual tabulation of the distribu- 

 tion of a large family of mollusks which has been undertaken for the 

 region under discussion and marks well the various subdivisions of 

 the larger provinces into which the contmental shelf fauna of the 

 west coast of America is divided. (See map, Plate 40.) 



They may be defined as follows: 



(1) ARCTIC. 



This extends from the summer limit south to the winter limit of 

 the pack ice, i. e., from the Sea-Horse Islands south to Hagemeister 

 Island. This region is characterized by 4 species belonging to 2 

 subgenera. (See first column of the summa^y^) 



(2) ALE una 



This embraces the Aleutian Islands, the Alaskan Peninsula, and 

 the main coast of Alaska with their adjacent islands south of Sitka, 

 and probably the inland straits south to DLxon Entrance. This 

 region is characterized by 19 species belonging to 5 subgenera; two 

 additional species are common to this and the next area. (See sec- 

 ond column of summar3\) 



(3) OREGONIC. 



This faunal area extends from Sitka, Alaska, south to Point Con- 

 ception, California, and probably south on the outside of San ^liguel, 

 Santa Rosa, and San Nicholas, and San Clemente Islands. It is 

 characterized by 70 species belonging to 14 subgenera. Eleven addi- 

 tional species extend over this and the next area. (See third col- 

 umn of summary.) 



(4) CALIFORNIC. 



This extends from Pomt Conception, California, south to Cape St. 

 Lucas, Lower California. It is characterized by 164 species belong- 

 ing to 27 subgenera. Two species are common to this and the next 

 area. (See fourth column of summary.) 



(5) MAZATLANIC. 



This extends from Cape St. Lucas, south to Acajutla, Guatemala. 

 It is characterized by 75 species belonging to 26 subgenera. No species 

 are common to tliis and the next area. (See fifth column of summary'.) 



(6) PANAMIC. 



This area extends from Acajutla south perhaps to Aguja Point, 

 Peru. It is characterized by 46 species, belongmg to 19 subgenera. 

 (See sixth column of summary.) 



(7) GALAPAGANIC. 



The fauna of these islands, though small, is absolutely distinct 

 and denotes a separate area. It consists of 5 species belonging to 

 5 subgenera. (See seventh column of summary.) 



