FAMILY TR1GLID.E GASTEROSTEUS. (Jy 



THE TWO-SPINED STICKLEBACK. 



Gasterosteus eiaculeatus. 



PLATE III. FIG. 9. —(CABINET OF THE LYCEUM.) 



Two-spinrd Slickhback. Pens. Arct. Zool. Suppl. (N'o description.) 

 Gaslerostnis biaciilcalus. MiTCH. Lit. ind Phil. Soc. Vol. 1, p. 430, pi. 1, (ig. 10. 



Characteristics. With two distant spines on the back, and a third near the dorsal. A strong 

 serrated spine on each side, representing tlie ventrals. Length 2* 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 Sijngnutluis. 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 strias 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 

 cmarginatc. 



Color. Dark olive-green above, gradually intermixing with light grecnisli and yellowish on 

 the sides. Fins more or less tinged with yellowish. 



Length, 2-5. Greatest depth, 0-5. 



Fmrays, D. 2.1.12; P. 9 ; V. 1 ; A. 1.8; C. 12. 



Fauna — Part 4. 9 



