2 ACANTHOPTERTGII. 



b. Two nostrils on each side. 



a. Spinous part of the dorsal fin considerably shorter than the soft-rayed part ; anal with 

 1 or 2 spines 6. SciJENiDiE. 



/3. Spinous part of the dorsal fin not shorter or not much shorter than the soft-rayed part. 

 * Ventral tins without scaly axillary processes. 

 Two dorsals, with VI-XVII, 8-17 rays; anal with I-II 6-12 rays .... 7. Percidji;. 

 A single dorsal, with X-XI 10-13 rays ; anal with III 8-12 rays .... 8. Centkarchid.e. 



** A scaly process at the base of the sj)ine of each ventral fin. 



A single dorsal with IX 10 rays; anal with IT-III 7-9 rays 9. Liognathid.e *. 



A single dorsal with X-XIV 10-18 rays; anal with III 7-13 rays . . . .10. PojiADASiDJi. 

 Two dorsals, with VIII, I 9-11 rays ; anal with III 6-7 rays 11. Centropomice. 



In all cases the account of the species is based on an examination of the examples 

 in the British Museum Collection ; but in the case of groups which have already been 

 adequately described a synopsis only is given, with references to the works in which 

 more details are to be found. 



Fam. 1. PLEURONECTID^. 



The Flat-fishes are a large family, at once distinguished from all other fishes by the 

 asymmetrical head, with the two eyes on one side. They are mostly marine, but many 

 ascend rivers for considerable distances. In Mexico and Central America four species 

 have been recorded as occurring in rivers above the regions aff"ected by the tides, and 

 must therefore be included in an account of the fresh-water fishes, 



1. CITHARICHTHYS, Bleeker, 1862. 



Citharichthys, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2678. 



Eyes on the left side. Mouth moderately largo ; each jaw with a single series of small pointed teeth ; palate 

 toothle.ss. Scales moderate or small, feebly ctenoid, deciduous ; lateral line nearly straight. Dorsal 

 commencing just in front of the eye and posteriorly free from the caudal; left ventral median, but not 

 continuous with the anal ; pectorals well-developed. 



1. Citharichthys gilherti, Jenkins & Evermann, 1SS8. 

 Citharichthijs yilberti, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2686. 



Depth of body about 2 in the length, length of head 3^ to 3j. iSuout as long as or a little longer than eye, the 

 diameter of which is 4.^ to 5| in the length of head ; interorhital region a narrow, shallow groove, bordered 

 by the slightly elevated orbital margins; maxillary extending to below middle of eye; gill-rakers of 

 moderate length, 12 to 14 on the lower part of the anterior arch. 38 to 45 scales in a longitudinal 

 series. Dorsal 77-85. Anal 57-63. Left pectoral as long or nearly as long as the postorbital part of 

 head ; right pectoral shorter ; caudal doubly truncate. Light brown, spotted or marbled with darker. 



Hah. Pacific Coast from Guaymas, Mexico, to Ecuador, entering rivers. 



My description is based on four specimens, 110 to 160 mm. in total length, from 

 * Usually known as Gerridic, a family name preoccupied in llemiptera. 



