16 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
of the pectorals, which appears to be a character of some importance, and which 
has led to the generic name of Aplodactylus, amounts in this specimen to six, 
being two more than was observed by M. Valenciennes in his, though the total 
number of rays in this fin is the same. I may also allude to the circumstance of 
the dorsal being invested at the base with a thickened membrane on each side, 
closely covered with small scales, which extends over nearly its whole length, 
but is most conspicuous along the spinous portion. This character is not men- 
tioned by M. Valenciennes. Neither does he mention the rows of minute scales, 
which occur between the rays of all the fins, except the ventrals. 
Mr. Darwin’s specimen of this fish is eleven inches in length. The following 
is the fin-ray formula : 
B62 Deans Ase: ©.17&c.57b. 9—vi; Viejo: 
1. Duues Aurica. Cuv. et Val. 
Dules Auriga, Cuv. et Val. Hist. des Poiss. tom. iii. p. 83. pl. 51. 
Form.—This species is remarkable for the prolongation of the third dorsal spine, which, in the 
present specimen, is not quite equal to half the entire length of the head and body ; a small 
portion, however, appears to have been broken off. The greatest depth is contained three and 
a half times in the entire length. The head, measured to the extremity of the opercular 
membrane, exactly equals the depth. The line of the profile is not quite straight, there being 
a slight depression at the nape, above which is a convexity in immediate advance of the dorsal 
fin. The lower jaw is a very little the longest. The eyes are large; and the distance between 
them barely equals their diameter. The other characters are exactly as stated in the “ Histoire 
des Poissons.” 
BY 6e DMi0/13--A. 3/7 C. 125 P17 VWs. 
Length 6 inches 3 lines. 
Cotour.—tThe recent colours are given by Mr. Darwin in his notes as follows : “ Sides with numerous 
waving longitudinal lines of brownish red; the intermediate spaces greenish-silvery, so figured 
as to look mottled. Head marked with lines of dull red and green. Ventral and anal fins dark 
greenish blue.”—He does not notice the vertical bands alluded to by Cuvier and Valenciennes, 
which are sufficiently obvious, and which accord with the figure and description of the authors 
just mentioned. 
Habitat, Maldonado Bay, Rio Plata. 
