86 
U. S. P R. R. EXP. AND SURVEYS—ZOOLOGY-GENERAL REPORT. 
The anterior dorsal spine is situated either in advance of the base of the pectorals or behind 
it, according to the species. The anterior margin of the anal is always provided with a small 
spine, similar to the one in advance of the second dorsal. The ventrals, which are abdominal, 
are composed of a stout, more or less serrated, spine, and a small soft ray, scarcely perceptible. 
The body is always very much compressed and sub-fusiform in its profile. The head 
constitutes sometimes the fourth, and sometimes the two-sevenths of the entire length. The 
upper surface is either smooth or corrugated ; the sides of the head are always smooth, no 
spines being ever extant upon the opercular apparatus. As to the sub-orbitals, they are sometimes 
entirely concealed under the skin. A narrow isthmus exists under the throat, separating the 
gill openings ; the branchiostegal rays are well developed, and three in number on either side. 
The investigator into the habits of these fishes will bear in mind the astonishing fact 
that a European species of this genus constructs a genuine nest into which the spawn is 
deposited and watched. It is related that the male is the sole architect in the construction 
of the nest; there are two openings to it, an entrance and an exit. At the breeding season 
the male compels the female to enter the nest, there to deposit her spawn, when, so soon 
as done, he drives her away, to come hack afterwards and keep a constant watch over the 
progeny, which otherwise would be eaten by the female. 
1. GASTEROSTEUS PLEBEIUS, Grd. 
Spec. Char. —Body partly plated ; peduncle of tail not keeled. Dorsal spines three ; of moderate development, and strongly 
serrated upon their edges, insertion of anterior one taking place immediately behind the base of the pectorals. Insertion of 
ventrals placed slightly in advance of the second dorsal spine ; ventral spine serrated on bolh edges, and its extremity not 
reaching the tips of the ossa innominata. Posterior margin of caudal fin sub-crescentic. 
Syn. — Gasterosteus plebeius, Grd. Proc. Acad. Nat. Sc. Philad. VII, 1854, 147. 
The largest of the numerous specimens of this species which we have examined measured 
about two inches, the head forming the two-seventh, or a little more, of that length. The 
upper surface of the head is corrugated, but apparently smooth as long as the slime rests upon 
it; its sides exhibit diverging minute granular ridges upon the opercular and sub-orbital bones. 
The lower jaw is slightly longer than the upper one, since it protrudes beyond it when the 
mouth is shut. The posterior extremity of the maxillary does not extend to a vertical line 
drawn across the anterior rim of the orbit. The teeth are exceedingly minute. The nostrils 
are nearer the orbit than the extremity of the snout. The eyes, circular and well developed, 
enter four times in the length of the side of the head by their diameter ; the distance between 
their anterior rim and the extremity of the snout is greater than one of their diameter. 
The greatest depth of the body, which corresponds to a vertical line drawn from the middle 
of the space between the first and second dorsal spines, enters about five times in the total length. 
The insertion of the first dorsal spine takes place immediately behind a vertical line drawn pos¬ 
teriorly to the base of the pectorals. When placed horizontally, its extremity stretches beyond 
the insertion of the second spine. The latter is larger than the first ; both are of but moderate 
development, conspicuously serrated, or rather prickly, upon both edges. The second spine, 
when brought horizontally backwards, does not reach the third and very small spines at the 
anterior margin of the second dorsal ; the distance, therefore, between the third and second 
spines is much greater than between the second and the first. The origin of the soft dorsal is 
nearly opposite the tips of the ossa innominata. The latter fin is sub-triangular, highest anteriorly, 
and diminishing gradually backwards ; it is composed of eleven, sometimes of thirteen, rays, 
the middle ones being bifurcated upon their extremity. The caudal fin, which constitutes about 
