436 Mr. C. T. Regan on the 



Gastrosteus aculeatus is found on the coasts and in tlie 

 livers of Northern Europe, Asia, and America, extending 

 soutliwards to the Iberian Peninsula, Northern Italy, the 

 Black Sea, the Santa Clara River in California, and New 

 Jersey. In the northern part of its range it is principally 

 marine, but further south seems to take less and less to the 

 sea ; finally, in Southern Italy, in Algeria, and in streams 

 south of the Santa Clara River in California it is represented 

 by three distinct permanently fluviatile species, which can 

 only owe their differentiation to the fact that they are not 

 now, and have not for some time been reinforced from the 

 ranks of the marine sticklebacks. 



As synonyms of G. aculeatus I include all the species 

 hitherto described, with the exception of G. algeriensis^ 

 Sauv. 



Gastrosteus aculeatus has III (II- V) 9-14 dorsal rays, 

 1 7-11 anal rays, and 31 to 33 vertebrae. The snout is 

 shorter tlian the postorbital part of the head, and the first 

 dorsal spine is inserted nearly above the base of the pectoral 

 fin and well in advance of the pelvic spine. The three species 

 which I recognize as distinct from it are : — 



1. Gastrostexis hologymnus^ sp. n. 



Gastrosteus argyropomus (non Cuv. & Val.), Giiiith. Cat. Fish. i. p. 4 

 (1859). 



Depth of body 4 in the length, length of head 3 to 3^ ( cJ ) 

 or 3f (?). Snout longer than eye, as lo»g as or only a 

 little shorter than the postorbital part of head ; diameter of 

 eye 4 in the length of head, interorbital width 4§ to 5. 

 Sides of body without bony plates ; naked area in front of 

 pectoral rather small ; pelvic plate notched in front, twice as 

 long as broad, i to f the length of head. Dorsal with 12 or 

 13 soft rays, anal with 8 to 10 ; origin of first dorsal spine a 

 little behind the base of the pectoral ; second spine ^ the 

 length of head ; pectoral extending beyond the vertical from 

 second dorsal spine; pelvic spines ^ to § the length of head. 

 31 or 32 vertebrae. 



Hah. Rome. 



Five specimen?, 55 to 60 mm. in total length. 



The complete absence of bony plates distinguishes this 

 form from the ggmnurus variety of aculeatus found in 

 Northern Italy, whilst the produced snout gives it quite a 

 different physiognomy. Were it not for this last ciiaracter 

 I should not regard this form as specifically distinct, as a 

 percentage of naked specimens occurs among the sticklebacks 

 of Santa Clara River in California. 



