150 



U. S. p. R. R. EXP. AND SURVEYS — ZOOLOGY GENERAL REPORT. 



has a double aperture, one of which being tubular. The branchial apertures are rather wide, 

 continuous under the throat ; the branchiostegals being six on either side. 



The origin of the dorsal fin corresponds to a vertical line which woukl intersect the anterior 

 rim of the pupil and slightly inflexed towards the left side. The rays increase in height 

 towards the jiosterior third of the fin to diminish again posteriorly, all being inclined backwards. 

 The anal has the same general structure and appearance, and terminates evenly with the dorsal 

 at a short distance from the base of the caudal, its origin corresponding to a line drawn imme- 

 diately behind the base of the pectorals. The latter are moderate sized and slender, the left 

 more so than the right one ; both having dichotomised rays, though less fully developed in the 

 left fin. The ventrals are rather small, inserted in advance to the base of the pectorals, and 

 extend somewhat beyond the anterior margin of the anal fin and, consequently, overlapijiug the 

 vent. Their middle rays are likewise dichotomised. The caudal fin, which is posteriorly 

 rounded or sub-convex, enters five times and a half in the total length ; its rays are simply 

 bifurcated without any further subdivision. 



Br. VI : VI ; D 74 ; A 59 ; C 3, 1, 6, 6, 1, 3 ; V 6 ; P 9. 



The scales on the right side are of but moderate development, longer than deep posteriorly, 

 ciliated or pectinated, some of them very conspicuously, others but slightly ; others still are 

 rugose over their entire exposed surface, being quite rough to the touch. Over the head and 

 opercular apparatus all the scales are of the rugose type. On the left side all the scales present 

 a smooth ajjpearance, and they do not extend over the dorsal, caudal, and anal fins, as is the 

 case on the right side. 



The color of the right side is uniform blackish brown ; the left side of a light brown. The 

 vertical fins are obsoletely maculated. 



List of specimens. 



PLEURONICHTHYS, Girard. 



Gen. Char. — Eyes rather large, situated on the right side. Interocular space very narrow. Head small. Mouth small, iu 

 gape being oblique, the jaws subequal, and the snout subtruncatcd . Teeth inconspicuous, occupying br>th sides of the jaws. 

 Origin of dorsal fin placed either in advance of the pupil, or else the entire orbit. Dorsal and anal fins not extending to the 

 caudal; latter posteriorly rounded. Scales small, cycloid in structure. Lateral lino slightly raised above the pectoral fins, 

 otherwise linear. 



Syn.— P<«uronic/i(/i!/s, Grd. in Proc. Acad. Nat. Sc. Philad. VII, 1854, 139. 



The body is rather deep, and in that respect resembling somewhat Rhombus, or else combining 

 the idea of Rhombus and Solea in its general outline. The sinallness of the head and mouth 

 are, however, characters which will at once enable a student to discriminate between these 

 genera. 



