Mr. Thompson on the Sticklebacks of Ireland. 95 



XIII. — On the species of Stickleback (Gasterosteus, Linn,) 

 found in Ireland. By Wm. Thompson^ Vice-Pres. Nat. 

 Hist. Society of Belfast. 



In the ^Histoire des Poissons' of Cuvier and Valenciennes, 

 the Gasterosteus acideatus of Linnaeus is divided into several 

 species. The viev^^s there adopted are followed in Great Bri- 

 tain * by Mr. Yarrell and Dr. Parnell in their respective works ; 

 but in Mr. Jenyns's ^ Manual/ four of these species — all that 

 have been recognised as British — are, after a close comparison 

 of examples from the same pond, and of these again with 

 others from different waters, reduced to one species f. Having 

 myself compared specimens of the fish in question from still 

 more numerous localities than the last-named author, I arrive 

 at the same conclusion in so far as it extends ; but go still 

 further, and venture to consider six or seven of the species of 

 the ^ Hist, des Poiss.^ as in reality but one, assuming so many 

 different appearances. To allude to the extreme accuracy of 

 description characteristic of that truly great work — the ^ Hist. 

 des Poiss.' — would be most superfluous. On anotlier point 

 altogether the different view adopted in the present paper 

 turns ; namely, on the permanency of characters there attri- 

 buted to the 3-spined Gasterosteus. 



In this genus, Ireland possesses all the forms which are in- 

 cluded in the British catalogue. An additional one — G. semi- 

 loricatus, Cuv. and Val. — will be particularly treated of, and 

 come first under notice, as one of the two varieties which are 

 protected with scaly plates throughout the sides. 



G. trachurus, Cuv. and Val., t. iv. p. 481. 



G. semiloricatus, Cuv. and Val., t. iv. p. 494. 



March 20, 1835. — On examination of a number of 3-spined 

 Sticklebacks from the island of Rathlin, (sent by Mrs. Gage 



* Nilsson, in his ' Prodromus Ichtliyologiae Scandinavica?,' published in 

 1832, thus describes varieties of Gasf. aculeaius, Linn. : — 



'* u.) Capite, a latere inspecto, magis acuto ; spinis dorsalibus longioribus, 

 media longitudinem capitis dimidiam sequante et dimidiam corporis altitu- 

 dinem superante. 



" /3.) Capite, a latere inspecto, magis obtuso ; spinis dorsalibus breviori- 

 bus; media multo breviore quam ^ capitis et dimid. corpor. altit." — p. 86. 



This author makes G. trachurus synonymous with G. aculeatus, Linn. — 

 he does not offer any opinion on the species of Gasterosteus in the ' Hist, 

 des Poiss.' 



t In a note to p. 350, Mr. Jenyns observes with reference to G. hrachy- 

 centrus, that " it is more than probable that some of the other foreign Gas- 

 terostei described by Cuvier are mere varieties of this species" — G. acii- 

 IcatuSy Linn. 



