NATURAL SCIENCES OF PHILADELPHIA. 501 



Synopsis of the SILLAGINOIDS, 



BY THEODORE GILL. 



Family SILLAGINOID.E Richardson. 

 Synonymy. 



Sillaginidae Richardson, Report of 15th Meeting B. A. A. S , 1846, p. 223. 



Gobioides part. Cuvier, Regne Animal, ed. i. 



Percoides part. Cuvier. 



Sillagoidei Bleeker. 



Sciaenoidei (Sillaginiformes) part. Bleeker. 



Trachinoidae part. Giiiither. 



The body is elongated and little compressed, highest under the first dorsal 

 fin, and thence nearly uniformly and slowly attenuated towards the caudal 

 peduncle, which is moderately slender. Scales of moderate or small size ; 

 their external margins are generally rounded and pectinated. Lateral line 

 simple, with a slight sigmoidal flexure and continued to the base of the caudal 

 fin, or even slightly between its median rays. Head oblong or elongated, 

 conical in profile, gradually decreasing in width above to the horizontally 

 rounded snout, and nearly plane below. Forehead flattened or little convex. 

 Eyes submedian. Nostrils double, approximated and in front of the eyes. 

 Suborbital bones not articulated with the preoperculum. Preorbital bone 

 very large, expanded over the side in front of eye, and entirely concealing the 

 ends of the maxillary bones. A ridge is continued obliquely from the posterior 

 suborbitals on the preorbital. Preoperculuin much longer than high, with a 

 prominent longitudinal fold, which, above the inferior horizontal border es- 

 pecially, is separated by a deep channel from the incurved portion which 

 forms the inferior flattened surface of the head. Operculum short and thin. 

 Interoperculum and suboperculum normally developed. Operculum with a 

 slight crest ending in a spine. Mouth small and terminal ; the periphery of 

 each jaw more or less semi-elliptical. Intermaxillary bones little protractile 

 downwards, with their ascending and marginal branches nearly equally de- 

 veloped. Supramaxillaries widest at their free ends and forming part of the 

 arcade of the mouth. Teeth on the jaws and the front of the vomer. Bran- 

 chiostegal membrane free, extending under the throat, but emarginated behind, 

 and concealed under the opercular apparatus. Branchiostegal rays six on 

 each side. Pseudobranchise present. Dorsal fins two ; the first short ; the 

 second elongated and equal to or little larger than the anal, with which it is 

 coterminal. Anal fin with two (or one) small spines. Caudal fin emarginated, 

 with its lobes rounded. Pectoral fins normally inserted on the humeral cinc- 

 ture, with the lower rays branched. Ventral fins thoracic, with one spine and 

 five branched rays. The fins have few or no scales. 



The skull is convex below, and has muciferous cavities like that of a Sciae- 

 noid. The pubic bones are well developed and separated from each other be- 

 fore by a sinus between the pedicles, by which they are suspended to the cora- 

 coid bones. There are thirty-four to forty-three vertebra?, of which twelve to 

 sixteen are costiferous. The stomach is cajcal ; the pyloric caeca few (2-5). 



The air bladder is simple. The ovaries are generally united nearly in a 

 single mass. 



This family is distinguished from all others by the combination of an elong- 

 ated body, and elongated and nearly equal second dorsal and anal fins, with 

 an oblong or elongated cavernous head, whose preorbital bones are very large, 

 and whose preoperculum is bent inwards below, covering the inferior surface of 

 the head, while a" crest or fold separated by a deep groove assumes the aspect 

 of the usual inferior margin. 



It manifests more or less resemblance to several families, but its true re- 

 lationship is rather difficult to be decided. 



1861.] 



