56 BULLETIN 150, UNITED STATES NATIONAL MUSEUM 



remote period to allow specific differentiation to take place. There 

 has been no recent intermigration between Asia and America, for the 

 species of the two regions are distinct. 



The distribution of the few North Atlantic species can readily be 

 accounted for by assuming that they migrated from Bering Sea 

 along the Arctic coast of America to the North Atlantic. Certain 

 species crossed over to northern Europe and others migrated down 

 the northeast coast of America to Connecticut. The species of the 

 two shores are different. Liparis liparis, a European species, has 

 been recorded from the New England coast, but the writer has been 

 unable to verify this record. Liparis atlanticus extends from Con- 

 necticut to Labrador, Liparis tunicata from Labrador to Greenland, 

 Liparis major from Greenland to the Kara Sea. The latter species 

 may be circumpolar. Liparis liparis and Liparis montagui are 

 European species. 



Assuming that the genus originated in the North Pacific the most 

 reasonable way by which we can account for the presence of species at 

 the southern end of South America is by migration along the American 

 coast line at some remote period when the tropical waters were suf- 

 ficiently cooled to offer a favorable environment. At the present 

 time a depth of 150 to 200 fathoms along the west coast of tropical 

 America affords a sufficiently cool temperature for these fishes. But 

 the genus is not represented there and is seems unlikely that the mi- 

 gration to the Antarctic has taken place under present conditions. 

 During the Ice Age, conditions were more favorable than now and 

 it was probably during this period that species of Liparis made their 

 way across the Equator. 



KEY TO SPECIES OF LIPARIS " 



A'. Peritoneum pale or silvery, usually with sparsely scattered brown or black 

 dots; pectoral in most of the species with more rays than the anal. 

 B^ Caudal free from the dorsal or connected for not more than one-fifth its 

 length; pectoral rays more numerous than the anal rays. 

 Ci. Dorsal notched; gill opening either above the pectoral or extending 

 |i.' I down in front of not more than 6 rays. 



D'. Anal less than 30; dorsal not more than 35; coeca less than 150. 

 E'. Gill slit above the pectoral, sometimes appearing to extend down 

 in front of the upper ray. 

 F'. Disk 2 or less in the head. 



G'. Pyloric coeca less than 50 (15-37); anterior dorsal rays some- 

 times elevated. American. 

 HI. Pectoral 26-29; no white bar at the base of the caudal. 



Atlantic montagui, atlanticus. 



H2. Pectoral 30-33; a white bar across the base of the caudal. 



Pacific rutteri. 



G". Pyloric coeca more than 50 (65-70) ; anterior dorsal rays never 



elevated. Asiatic curilensis. 



F^. Disk more than 2 in the head cally odon. 



grebnitzkii. 



la See supplementary key for North Atlantic species. 



