84 
ACANTHOPTERY GII . 
ventral spines, and in the lateral plates. In some individuals these do 
not occupy more than the central portion of the sides, in others the whole 
sides, and again are intermediate. 
In the absence either of a specimen for comparison, or a figure to refer 
to, it may perhaps be considered that certainty cannot be arrived at re- 
specting G. semiloricatus. This fish is stated to differ from G. trachurus 
in having only 22 or 23 plates on each side to the origin of the caudal 
keel instead of its 25 or 26, and in the shoulder-plate (plaque de l’epaule) 
being larger. It has been seen that some of my specimens, and of these 
some of the largest size, possess only the number of lateral plates attri- 
buted to G. semiloricatus. In examples of equal length, and from the 
same as well as from different localities, I find the size of v the shoulder- 
plate to vary like other characters. Hence I am disposed to regard some 
of the examples under consideration as this fish. 
In the Hist, des Poiss. it is remarked of G. semiloricatus, “Nous n’avonspu 
trouver aux environs de Paris que des epinoches a queue nue ; il nous en est 
venu de pareilles des departemens de la Somme et de 1’ Oise, de la Rochelle et 
de quelques autres lieux : nous avons observe celle a queue cuirassee dans les 
ruisseaux des cotes de Normandie, et encore recemment M. Deslongchamps 
nous l’a envoyee de Caen, et M. Baillon en a pris dans le Hable-d’Ault, lac 
saumatre de l’embouchure de la Somme, pres du Treport. C’est la seule qui 
se trouve dans les etangs des environs de Berlin, et elle y est en quantite innom- 
brable. Peut-etre est-ce l’espece qui habite plus frequemment pres des bords 
de la mer, et qui peut entrer dans l’eau salee. Des observations ulterieures 
nous apprendront sans doute bientot ce qui en est.” — t. iv. p. 494. 
This accords generally with my own observation, as in seven out of 
the nine localities whence my specimens mailed throughout the sides 
were derived — whether they be called G. trachurus or G. semiloricatus — 
they were taken either in the sea or estuary. The exceptions are the 
largest specimens, which were procured in a “ pool of brackish water ac- 
cessible to -the sea ; ” and those from Rathlin, obtained in fresh water. 
From the passage just quoted, we learn that the G. semiloricatus inhabits 
the pools about Berlin. It has always seemed to me not improbable, that 
in the sea, where the enemies of this diminutive fish are more numerous 
than in the fresh water, the protecting hand of Nature had as a defence 
armed its body with these lateral plates. That some fishes have the 
power of accommodating their colour to that of the ground or bottom of 
the water they frequent, and are thus rendered comparatively inconspicu- 
ous to their enemies, is well established. 
A third species of 3-spin ed stickleback, armed throughout the sides 
like those here treated of, is the G. Noveboracensis, which, as its name 
denotes, is found at New York. Judging from the description and figure 
of this fish in the Hist, des Poiss., I should not consider it distinct 
from G. trachurus or G. semiloricatus. The specimens which have come 
under my examination differ much in the few characters which are said to 
distinguish this fish from G. trachurus. The high position of the lateral 
line is the chief character of G. Noveboracensis ; in some specimens be- 
fore me this line is so near the back that three-fourths of the body of the 
fish are below it. Our G. Pungitius is admitted as an American species 
by Hr. Storer in his interesting work on the Fishes, &c., of Massachu- 
setts (p. 32), and for a copy of which I am indebted to his kindness. 
The descriptions and figure of the G. obolarius, Cuv. and Yal. — a 3- 
spined stickleback armed throughout the sides, and found in the North 
Pacific Ocean and the Gulf of Kamtschatka — are said in the Hist, des 
