90 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



As regard to the plates on the sides of the body, their number and arrangement is the same 

 as in the preceding species. 



The ground color of the dorsal region is greyish, rendered almost black by crowded dots of 

 the latter hue ; the sides are lighter and silvery. The base of the caudal fin is marked by a 

 transverse jet black band, sometimes reduced to two patches, one to either lobe. 



List of specimens. 



4. GASTEROSTEUS INOPINATUS, Grd. 



SPEC. CHAR. Body partly plated ; peduncle of tail consequently not keeled. Dorsal spines three, slender, and slightly serrated 

 upon their edges, insertion of the anterior one taking place above the base of the pectorals. Insertion of ventrals placed imme 

 diately in advance of the second dorsal spine ; ventral spine serrated on both edges, but less conspicuously below than above, and 

 its extremity terminating about evenly with the tips of the ossa innominata . Posterior margin of caudal fin sub-crescentic. 



SYN. Gasterosteus inopinatus, GRD. Proc. Acad. Nat. Sci. Philad. VII, 1854, 147. 



In many respects this species might be considered more closely allied to Cf. plebeius than either 

 G. serratus or G. intermedius. In the first place, the anterior or thoracic region alone is plated ; 

 the insertion of the ventrals in advance of the second dorsal spine is another similarity between 

 it and G. plebeius. 



The general aspect is slender, elongated, considerably tapering from the origin of the anal 

 backwards ; the peduncle of the tail especially is long and slender. The greatest depth of the 

 body, measured across the origin of the ventrals, is contained five times in the entire length. 

 The head itself constitutes the fourth of the same length. The eyes are large and circular, and 

 their diameter is contained three times and a half in the length of the sides of the head, exactly 

 once in advance of their anterior rim. The mouth is somewhat smaller than in G. plebeius, 

 equally oblique, but the lower jaw is less protruding beyond the upper. 



The anterior dorsal spine, which is inserted immediately above the base of the pectorals, does 

 simply reach the base of the second spine when brought horizontally backwards. Furthermore, 

 there are instances in which it does not extend even so far. The tip of the second spine leaves 

 quite a space between it and the third spine. The spines themselves are very slender and acute, 

 and not, or but slightly, serrated upon their edges. The origin of the second dorsal takes place 

 quite posteriorly to a vertical line intersecting the tips of the ossa innominata. The beginning 

 of the anal is situated opposite the fifth or sixth soft ray of the second dorsal, the middle rays 

 of both of these fins being bifurcated. The posterior rays terminate evenly, at a considerable 

 distance from the base of the caudal fin. The anal spine is very exiguous. The caudal fin, which 

 constitutes the seventh of the total length, is concave posteriorly, composed of ten bifurcated 

 and two undivided rays, with rudimentary ones above and below. The insertion of the ventral 

 spine takes place immediately in advance of the second dorsal spine ; it is minutely serrated on 



