1903.] FISHES FROM RIO JANEIRO. 63? 



Air-bladder large, with two long lateral horns anteriorly and 

 with a series of compartments along each side : anteriorly 

 attached by a sti'ong unpaired muscle running forward above the 

 cesophagus. 



Mylacrodon goeldii, sp. nov. (Plate VII.) 



Depth of body 2|-24 times in total length, length of head 3|- 

 3|- times. Snout as long as eye, the diameter of which is 4 times 

 in the length of head, interorbital width 3^ times. Lower jaw 

 included within the upper ; maxillary extending to below anterior 

 quarter of eye ; prteorbital entire. 1 2-1 3 gill- rakers on lower part 

 of anterior arch. Sc. 55-60 ^^ ; upper part of head, cheeks, and 

 opercles scaly; snout, jaws, and prseorbital naked. D. XI, I 13, 

 commencing somewhat behind the axil, first spine very small, 

 second short, third longest and equal to |— | the length of head, 

 thence decreasing ; aiiterior soft i-ays longest, equal to seventh 

 spine. A. Ill 10, first spine short, third |-| of the length of 

 second, which is equal to half the length of head. Pectorals scaly 

 at the base, |— | the length of head, ventrals a little longer, not 

 extending to vent ; caudal strongly emarginate. Dark grey above, 

 silvery below, fins blackish. 



Description based on two examples from Rio Janeiro, 225 and 

 230 mm. in total length. 



Gerrid^, 



The East Indian genera Gazza Riippell and Liognathus Lacep. 

 (^Uqtmla Cuv.), until now placed with or near the Carangidse, are 

 without doubt veiy nearly allied to Gerres, which they most closely 

 resemble not only in external features but also in their internal 

 anatomy. The relations of the genera of this family ai-e shown 

 in the subjoined key : — 



A. Scales moderate or large ; gill-membranes free from 



the isthmus. 



D.IX-X 10; A. 11-1117-9 1. Gerres Cnvicr. 



D. IX-X 15-16; A. V 13-14 2. Fentaprioii Blaeker. 



B. Scales small ; gill-membranes narrowly joined to 



isthmus ; D. VIII 15-16. A. Ill 14. 



Teeth in jaws minute 3. Lior/nathns Lacepede. 



Teeth in jaws rather strong, compressed, pointed... 4. Gazza Riippell. 



The distinction of the species of the genus Gerres is a matter of 

 some difficulty. Dr. Goeldi's collection includes examples of a 

 Gerres belonging to the section with prseoperculum and prfeorbital 

 serrated and with dark longitudinal lines along the rows of scales, 

 and which I identify with G. patao Poey. Nearly all the 

 American species of this section resemble each other very closely 

 in proportions of the head and body, size of the eye, extent of the 

 mouth, and number of scales and fin-rays ; and it appears that 

 the most constant characters which can be used for specific dis- 

 tinction are the number of gill-rakers, the length of the second 



