GASTEROSTEUS.] PISCES (OSSEI) ACANTHOPT. 349 



Back and sides olivaceous, sometimes passing into yellowish brown or 

 dusky blue: throat and breast, in some individuals, bright fiery red: 

 belly and flanks silvery, with a pearly lustre. 



Var. a . G. trachurus, Cuv. Yarr. in Mag. of Nat. Hist. vol. in. 

 p. 522. fig. 127. a. Rough-tailed Stickleback, Yarr. Brit. Fish. vol. i. 

 p. 76. The scaly plates extending the whole length of the sides; in 

 number about thirty. 



Var. j3. G. semiarmatus, Cuv. Yarr. in Mag. of Nat. Hist. vol. in. 

 p. 522. fig. 127. b. Half-armed Stickleback, Yarr. Brit. Fish. vol. i. p. 80. 

 Lateral plates extending to a vertical line joining the vent and com- 

 mencement of the soft dorsal ; in number from twelve to fifteen. 



Var. y. G. leiurus, Cuv. Yarr. in Mag. of Nat. Hist. vol. in. p. 522. 

 fig. 127. c. Smooth-tailed Stickleback, Yarr. Brit. Fish. vol. i. p. 81. 

 Lateral plates from four to six; extending only as far as the pectoral 

 fins, when these last are laid back. 



Var. d. G. brachycentrus, Cuv. ? Short-spined Stickleback, Yarr. 

 Brit. Fish. vol. i. p/82. Lateral plates not extending beyond the pec- 

 torals : dorsal and ventral spines very short. 



Common throughout the country in rivers and streams, as well as in 

 stagnant waters. Is also found occasionally in the sea. Of active and 

 lively habits. Is very voracious, and preys on worms and aquatic insects. 

 Spawns, according to Bloch, in April and June ; according to Cuvier, in 

 July and August. 



Obs. The above species is subject to great variation, not only in the 

 number of the lateral plates, but in several other less obvious respects. 

 The former may occasionally be found of every intermediate number 

 between that which characterizes the G. leiurus, Cuv. and that which 

 appears in the G. trachurus of the same author. This number, moreover, 

 is sometimes found constant in specimens which differ remarkably in 

 other respects ; at other times, varying, when all other characters remain 

 the same. From these circumstances combined, I feel satisfied that the 

 above are mere varieties, notwithstanding the high authorities on which 

 they stand recorded as distinct species. Perhaps it may be useful to state 

 the result of a close comparison of a large number of individuals with 

 each other from different localities. 



(1.) Specimens from the Thames, procured by W.Yarrell, Esq. These 

 agreed in having the eyes very large; the space between rugose, with 

 granulations disposed in lines ; the teeth rather prominent ; the osseous 

 disk between the opercle and pectoral large ; the lateral plates varying in 

 number, but well-defined and very regularly disposed ; the ventral plate 

 narrow, more than twice as long as broad at the base ; the dorsal and 

 ventral spines long, the latter equalling two-thirds of the depth of the 

 body, nearly straight, and often with serrated edges ; sides of the tail 

 generally, but not always, carinated. 



(2.) Specimens from Wilbraham in Cambridgeshire. Depth greater 

 in proportion to the length than in no. 1 ; eyes much smaller ; the rugose 

 lines between as before ; teeth similar ; osseous disk behind the opercle 

 much smaller; lateral plates few in number but well-defined; ventral 

 plate very large, its breadth at the base contained only once and a half in 

 its length ; spines, the ventral especially, nearly as long as in the above, 

 equally serrated, but not so straight, being slightly curved from their 

 base; sides of the tail perfectly smooth. 



(3.) Specimens from the pond in the Botanic Garden, Cambridge. 

 Eyes intermediate in size between those of nos. 1 & 2, but varying 

 slightly in different individuals ; rugose lines on the vertex generally 

 indistinct, sometimes wholly wanting with the exception of two, one 



