FAMILY TRIGLID4® — GASTEROSTEUS. 65 
THE TWO-SPINED STICKLEBACK. 
GASTEROSTEUS BIACULEATUS. 
PLATE Ill. FIG. 9.—(CABINET OF THE LYCEUM.) 
Two-spined Stickleback. PENN. Arct. Zool. Suppl. (No description.) 
Gasterosteus biaculeatus. Mutcn. Lit. and Phil. Soc. Vol. 1, p. 430, pl. 1, fig. 10. 
Characteristics. With two distant spines on the back, and a third near the dorsal. A. strong 
serrated spine on each side, representing the ventrals. Length 24 inches. 
Description. Body compressed, tapering away to a very small caudal extremity. Body on 
each side covered by a series of from twenty-eight to thirty narrow vertical plates, striated 
perpendicularly on their surface, and faintly denticulated on their posterior margins. Vent 
with an anterior pouch, analogous to that observed in Syngnathus. The course of the lateral 
line near the back is indicated by a series of prominences, finally terminating on the carinated 
side of the tail. This carina is high and membranous, and when viewed from above, resem- 
bles lateral finlets. The humeral bone terminates above the base of the pectorals, in a flat 
point. The ventral spine on each side is 0°3 long, acute, serrated on each side, with a 
prominent flattened process on each side of the base. A flat lustrous silvery plate between 
the pectorals and the branchial orifice. Head flattened above, with numerous impressed 
punctures arranged in rows. Eyes large. Nostrils midway between the latter and the point 
of the jaw. Teeth exceedingly minute, with a broad velum across the upper jaw. The place 
of the first dorsal occupied by two distant, slightly curved, compressed spines, serrated on 
their edges, and each furnished behind with a short membrane ; a third, similar in shape, 
but smaller, near the dorsal fin; all are much enlarged at their bases ; the anterior two 0°3 
long, the posterior 0° 1. 
The dorsal fin longer than high; its anterior rays longest, composed of one spine and 
twelve simple rays. Pectoral fins elongated, and containing ten rays. The ventrals repre- 
sented by a single spine on each side, as described above. Between these spines is a long 
triangular plate, with a central elevated ridge ; its surface striated transversely in front, with 
angular strie behind, and terminating in a sharp point, as represented in the plate ; its use 
appears to be, to support the abdominal pouch. The anal fin commences posterior to the 
origin of the dorsal, and is longer than high, slightly excavated on its margin, and contains 
one bent short spine and eight rays. The caudal fin contains twelve rays, and is slightly 
emarginate. 
Color. Dark olive-green above, gradually intermixing with light greenish and yellowish on 
the sides. Fins more or less tinged with yellowish. 
Length, 2°5. Greatest depth, 0°5. 
Fin rays, D. 2.1.12; P.9; V.1; A. 1-8; C. 12. 
Fauna — Parr 4. 9 
