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17. S. P. R R. EXP. AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
2. GASTEROSTEUS SERRATUS, Ayres. 
Spec. Char. —Body entirely plated ; peduncle of tail keeled. Dorsal spines three, high and slender, conspicuously serrated 
upon their edges ; anterior one inserted a little in advance of the base of the pectorals. Insertion of ventrals situated somewhat 
in advance of the second dorsal spine, their own spines being serrated upon both edges, more conspicuously above than below, 
and extending beyond the tips of the ossa innominata. Posterior margin of caudal fin concave. 
Syn— Gasterosteus serratus , Ayres, Proc. Cal. Acad. Nat. Sc. I, 1855, 47. 
Closely allied to the preceding is G. serratus; indeed, the only striking chracteristic consists in 
the presence of bony scutellae along the whole length of the flanks. The few specimens before 
us measure a little more than two inches, the head forming the fourth of the entire length. 
The upper surface of the head, the opercular and sub-orbital bones, are finely granular. The 
nostrils are situated midway between the anterior rim of the orbit and the extremity of the 
snout. The eyes are large and circular, their diameter entering three times and a half in the 
length of the sides of the head, exactly once in advance of their anterior rim. The dorsal spines 
are slender, and higher than in the preceding species; the second is a little larger than the 
first, and both are conspicuously serrated upon their edges. The first spine, when bent hori¬ 
zontally backwards, extends a little beyond the second, whilst the latter, in a similar position, 
reaches the base of the third and very small spine at the anterior margin of the second dorsal 
fin. The first dorsal spine is situated above the base of the pectorals. The origin of the second 
dorsal takes place anteriorly to a vertical line met by the tips of the ossa innominata; it is 
composed of eleven rays, the middle ones of which, bifurcated. The origin of the anal takes 
place under the fifth of the second dorsal, and terminates evenly with the latter at a short 
distance from the base of the caudal. The rays, nine in number, besides the anterior spine, 
have the same structure as those of the second dorsal. The caudal is posteriorly sub-crescentic, 
or concave, constitutes about the seventh of the total length, and composed of ten bifurcated and 
two undivided rays, together with many rudimentary ones. The insertion of the ventral spine 
is situated entirely in advance of a vertical line passing before the second dorsal spine ; it is 
elongated, slender, acerated, projecting beyond the tips of the ossa innominata , and reaching 
the vent. The serratures or prickles of its upper edge are much more developed than upon the 
lower. The pectoral rays are slender, but all well developed, though undivided, constituting 
a broad fin, exteriorly sub-convex. 
Br. Ill: III; D I, I, I, 11; A I, 9 ; C 5, 1, 5, 5, 1, 4 ; YL1; P 10. 
As already stated, the sides of the body are provided with a series of thirty-two to thirty- 
three plates, or scutellae, extending from the supra-scapular region to the base of the caudal 
fin. The three anterior are supra-scapular altogether, small and irregular ; the next twenty- 
five are transversely elongated, occupying the middle of the flanks, whilst the four or five 
remaining ones constitute a sharp ridge along the peduncle of the tail. The surface of these 
scutellae is granular, in diverging lines from a central point on each plate. There is an 
abdominal and a dorsal area, which are not covered by the extremities of the lateral plates or 
shields. 
Ground color, greyish brown above, with numerous minute blackish dots ; dorsal region 
darker than the sides ; abdominal region lighter; a blackish band along the keel on the 
peduncle of the tail. 
A specimen of this species from the marshes of the bay of San Francisco, labelled by Dr. 
Ayres himself, leaves no doubt as to its identity; it was brought home by Dr. John S. New- 
