86 
ACANTHOPTERYGII. 
brown colour, which is continued down the sides in the form of regular 
transverse bands upon a yellow ground ; — River Shannon, at Killaloe 
(Rev. C. Mayne) ; — Youghal, County Cork (Dr. Ball). 
From Scotland I have specimens obtained in the neighbourhood of 
Portpatrick by Capt. Fayrer, R. N. Examples from the Thames have been 
favoured me by Mr. Yarrell ; and in the river Learn, at Leamington, 
Warwickshire, the G. leiurus has occurred to myself. Next to this 
variety naturally comes the 
G. brachycentrus, Cuv. and Val., t. iv. p. 499, which, like it, is smooth 
along the sides from the pectoral region, but differs in the shortness of the 
dorsal and ventral spines. From the comparative length of these spines 
alone do I distinguish the two varieties, the other characters attributed 
to G. brachycentrus being ever varying. The Irish localities whence I 
have this fish are the neighbourhood of Belfast, and pools along the margin 
of Lough Neagh (W. T.), Dublin, Youghal, and Portarlington — supplied 
from these three localities by the friends before mentioned. 
The largest example which has come under my observation was one 
taken by myself in England, at Stow Pool, Lichfield, in July, 1836, and 
which was noticed in the Proceedings of the Zoological Society for the 
next year. This is the only allusion I have seen to the G. brachycentrus 
in Great Britain. 
This variety, which from the shortness of its spines is the most defence- 
less of the 3-spined sticklebacks, we should, d priori, — i. e. if the sugges- 
tion respecting the full-armed variety be correct, — expect to find where it 
has fewest enemies, and such, according to my very limited observation, 
is the case. This would seem to be the variety more peculiar to still 
water, in which it often attains a very large size. The only continental 
notice of this fish known to me is that in the Hist, des Poiss., where it 
is stated to have been obtained by M. Savigny in the brooks of Tuscany. 
The following comparison between G. brachycentrus from the neigh- 
bourhood of Belfast, and specimens of G. leiurus, & c., from the Thames, 
with which I have been favoured by Mr. Yarrell, was drawn up early in 
1834, and read before the Linnsean Society that year.* 
In the form of outline the Irish fish generally differs much from the 
G. leiurus, the latter being from the centre of the back alike gracefully 
sloped on either side to the head and tail, giving that part a handsome 
and finely-arched appearance : the under side of the body also exhibits 
more of this form than that of its congener. The back of the Irish species, 
instead of thus sloping gradually to the centre, is at that part rather flat, 
and is at least as high where the dorsal fin originates as elsewhere. The 
Irish fish is in proportion to its depth longer than the G. leiurus, as speci- 
mens of the latter under 2|- inches in length, when compared with Irish 
specimens 3 inches long, proved of equal dimensions (8 lines) at the deep- 
est part. The difference is also strongly marked in the relative breadth 
of the two species, the Irish maintaining considerable breadth throughout, 
even to the origin of the caudal fin. The teeth in the lower jaw of the 
Irish species consist in the centre of about four rows irregularly disposed, 
but become gradually less numerous towards the back of the mouth, 
where they terminate in a single line : the upper jaw contains three 
rows in front, the outer and inner being regular in distribution. In num- 
ber, the G. leiurus which I examined does not possess so many teeth as 
that species, but in their arrangement there is little difference. On 
* Phil. Mag. vol. v. 299 (1834). 
