86 U. S. P R. K. EXP. AND 8UKVEYS — 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 tlie 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 

 si>ine8 being ever e.xtant 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 tiie 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 back 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 thrte ; 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 both edges, and its extremity not 

 reaching the tips of the ossa innominata. Posterior margin of caudal fin sub-crescentic. 



Sm.^Gasterosteus plebeiui, Gun. Proc. Acad. Nat. Sc. Pliilad. 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. Tlie 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 t'nnoTOinaia. 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 



