On the Species of Three-spine J Sticklebacks. 115.5 



Cau.lal cl»*o|)ly forked, tlu' l<)n;,a'.sl rays bring twice as loii;^ as 

 I lit* shortest. 



Colour greenish biowti above, sides atid lower parts silvery. 

 A few scattered dark spots on upper half of body. 



One spcciinejj (ca. r>()0 mm.) from the Indus near Lch. 



Ij. — The Sfifriea of' Three-sptned Stickh hitcka 

 (Uastiosieiis). By C Tatk Ki:(}an, M.A. 



I :iAVE recently made a study of the Three-spined Stickle- 

 backs {(iaslrosteux) in the British ^rust-um, with a view to 

 determining the nunil>er of species which may be recogtsized. 

 After examination of a large number of s|)ecimens, reprr- 

 aenting all the nominal species which have been (lescril)ed, I 

 have arrived at the conclusion that the greater part of the 

 area of the genus is occupied by a single species, 0. aculeatus, 

 which is very variable. In the northern part of its range in 

 the sea the ilermal ossilieatiun is ytiong, the series of bony 

 ])lates com|)lete, the caudal keel prominent, the ectocoracoids 

 long and the naked areas above them consequently large, 

 the j)elvic plate long, lanceolate, without an anterior notch, 

 Hnd the fin-spines usually either long or strong. Towards 

 the southern part of its range in the sea, or in fresh water, 

 the dermal ossification is weaker; if the bony plates form a 

 complete series they are not so deep nor usually so numerous 

 as in northern marine examples, and the caudal keel is less 

 prominent ; the series of plates may be incomplete, the first 

 to disappear being the ones preceding the caudal keel, the 

 most persistent being the three (5th to 7th) which are 

 usually in contact with the ascending process of the pelvis ; 

 i«ometimes the plates are entirely absent. The jjclvic jjlate 

 becomes shorter and may develop an anterior notch, becoming 

 heart-shaped, arrow-shaped, or even V-shaped ; also tho 

 naked area in front of the pectoral fin may become smaller, 

 the spines shorter or weaker, and the fin-rays moro or less 

 reduced in number. 



I am unable to detect any difl!erence between specimen-* 

 from the Atlantic and Pacific: for example, fully-mailed 

 specimens from Puget Sound appear to me to be in every 

 way identical with 8on)e from the Shetlaruls ; similarly, 

 specimens from the Santa Clara River, (!alifornia, agree 

 closely with others from various inland localiiies in the 

 British Isles, from Noithtrn Italy, and from Jajtaii. 



