116 Dr. C. F, Liitken on the Changes of Form in Fishes 



Leaving out of consideration Argyreiosus dorsalis^ with regard 

 to which I will not attempt to decide Avhether it is a variety of 

 Selene setipinnis or a distinct species, it seems to me evident, 

 from all that I know in nature and from literature, that in- 

 stead of four species there are only two on the east coast of 

 America, namely Selene [Argyreiosus] vomer ^ Linn., and S. 

 setipinnis^ Mitch. [Vomer Brownii). I have illustrated by 

 two series of figures (pp. 543 and 547 of the Danish memoir) 

 the development of these two species and the changes they 

 undergo with age. The young form of 8. setipinnis has been 

 described under the name of Argyreiosus unimaculatus ; if 

 consistency had been desired it might have been set up as a 

 distinct genus ; the very old form of the same species is Platy- 

 somus micropteryx of Swainson. Argyreiosus vomer ^ L., Zeus 

 rostratus and Argyreiosus capillaris of Mitchill, A. ■Spixiiy 

 Cast., triacanthus and Mauricei^ Sw., and senegalensisj Guich., 

 are all one and the same species, Selene vomer (L.), which, 

 in its complete development, is represented by the Selene 

 argentea, Lac, described by Brevoort. The two species 

 attain nearly the same size (2 feet), and follow a very parallel 

 course in their evolution — with this reseiwation, however, that 

 the successive stages present greater differences among them- 

 selves in S. vomer than in S. setipinnis, and that the principal 

 changes are earlier accomplished in this latter species. As 

 will be seen from the figures, the young forms of the two 

 species have the body very short and thickset ; the first dorsal 

 and the ventrals are well developed, and have filamentous 

 prolongations in S. vomer ; with age the body extends more 

 or less in length, and the ventrals as well as the first dorsal 

 are reduced to a minimum, while the pectorals become elon- 

 gated, and the first ray of the anal and that of the second dorsal 

 acquire an enormous length, in S. vomer. Thus, in propor- 

 tion as the form of the body is modified, the prolongations of 

 the fins which in the young perform the office of instruments 

 of movement or of balancement, are replaced in the adults 

 by prolongations of the same nature, but developed elsewhere. 

 Both species occur on the west coast of Africa, and they have 

 also been met with on the west coast of America. I must, 

 however, remark that the species from Nicaragua possessed 

 by our museum, and which there represents S. vomer ^ is a 

 distinct species [S. Oerstedii, m.), distinguished by a peculiar 

 profile and by the number of its rays (D. 8 . 1 . 18 ; A. 1 . 15). 



13. Zeus; Zenopsis (Lampris; Mene). 



A critical comparison of the materials in the possession of 

 our museum, in the form of fishes from St. Pierre, in the 



