40 



CAMFOKNIA ACADEMY OF SCIENCES 



72. Opisthonema libertate (Gi'tnther). 



Abundant; several specimens preserved averaging about 25 cm. long. Young 

 specimens were also seen at Acapulco. 



This species differs from 0. oglinuni in coloration, in the shorter dorsal and 

 anal fins (the latter containing 20 or 21 rays), and in the more numerous gill-rakers. 

 The alleged differences in length of head are not reliable, both species varying greatly 

 in this resj^ect and no average difference being evident. 



Six specimens of 0. libertate give the following measurements: — 



In addition to the details of coloration already reported there is frequently 

 present a series of small, round, evenly-spaced dark spots, behind the humeral spot, 

 along the line separating the blue of the back from the silvery of the sides. Scutes 

 18+14 or 15. 



73. Ilisha furthi {Sleindachnev). 



Pcllona furthi Steindachner, 1875a, p. 14. 

 Pcllona panamcnsis Steindachner, 1. c. p. 14. 



A very abundant food-fish at Panama, but of inferior quality. The species is 

 extremely variable in shape, but the deepest forms with strongly arched ventral out- 

 line {I. furthi) grade imperceptibly into the more slender forms with weak ventral curv- 

 ature (/. 2^nna mentis). No other characters are correlated with this difference in ventral 

 curvature, and it appears certain that but a single species is represented. The deeper 

 specimens are constantly the smaller ones, so far as indicated by the material at hand. 

 The eye is therefore projwrtionately larger, and the snout (measured into the eye) 

 apparently shorter than in the larger, slenderer individuals. In none of the 

 specimens do the first five to seven anal rays originate under the dorsal fin, as describ- 

 ed in I. furthi. In both deep and slender forms the first anal ray is approximately 

 under the last of the dorsal. The front of the dorsal is constantly nearer the tip of 

 snout than the base of the caudal, the difference varying from f to f diameter of orbit. 



The following table of measurements exhibits the variation in depth of body, 

 and in size of eye and snout. The length into which the depth of body is meas- 

 ured, is taken from tlie tip of snout to base of caudal, excluding the projecting tip of 

 lower jaw. Steindachner has apparently included the latter in his measurements. 



