GonostomatIdae—--GKEY 
469 
Fig. 5. Argyripnus atlanticus, standard length 35.5 mm., ventral view. 
and between group of (5) and posterior AC 
group 3.5-4. 
Premaxillary more than half as long as 
toothed portion of maxillary. Maxillary reach- 
ing a vertical from posterior margin of eye. 
Head and trunk shorter than tail. Anal origin 
slightly in advance of dorsal origin, which is 
above a vertical from about third anal ray. Adi- 
pose fin well developed, its origin above a verti- 
cal from just behind Ac group of ( 5 ) . Pectoral 
fin long, nearly reaching anal origin. Ventrals 
inserted well in advance of dorsal origin, ends 
of rays broken. 
BR (6). IV (6) + (11) = 17, first organ of 
abdominal group directly below last organ of 
isthmus group, which curves upward posteriorly; 
individual organs of first group slightly larger 
than those of abdominal group. VAV-AC (21) 
+ (5) + (17) = 43, first 7 in front of anal fin 
and larger than remainder, upward curve over 
anal fin low and gradual. IC 60. OA ( 2 ) + 3 = 
5 on left side, no damage apparent, probably not 
fully developed; ? + 4 on right side, first organs 
lost but gland remaining (possibly contained 
2-3 photophores ) . 
Color in alcohol yellowish; diffuse brown pig- 
ment on caudal peduncle and nape; 3 irregular 
series of small black chromatophores from nape 
to caudal. 
These two little fishes are considerbly smaller 
than any specimens of the genus Argyripnus 
previously reported and provide the first scant 
evidence of developmental changes. The larger 
one possibly possesses all adult characters but it 
seems more likely that the OA are still in- 
complete and that a few of the organs of the 
first VAV-AC group have not yet developed. One 
or 2 additional organs may also appear in the 
last group of AC, which in this little fish begins 
directly behind the anal fin. In all other speci- 
mens of Argyripnus seen or figured there are 2 
to 4 of these photophores above the end of the 
anal fin. 
Characters of the smaller specimen suggest 
that the middle group of 5 AC develops relatively 
early and that of the anterior VAV-AC group the 
organs in front of the anal fin appear first. In 
the last group of AC the posterior organs are 
apparently first to appear. The OA develop late, 
probably being still incomplete on the 35.5 mm. 
specimen. If the isthmus IV are actually straight 
on the small damaged fish, as they appear to 
be, the displacement upward of the posterior 
organs would occur after the species reaches a 
