1863.] mr. j. y. johnson on new fishes. 403 



8. Descriptions of Three New Genera of Marine Fishes 



OBTAINED AT MADEIRA. By JaMES YaTE JoHNSON, CoRR. 



Mem. Z. S. 



(Plate XXXVI.) 



Order ACANTHOPTERYGII. 



Fam. Carangid^, Giinther. 



Diretmus, gen. nov. 



Body much compressed and elevated, covered with small spinous 

 scales. Abdomen prominent and keeled. Mouth large, non-pro- 

 tractile ; minute pointed teeth in the jaws, none on the palate ; a pair 

 of large tooth-like bony processes projecting from the anterior ends 

 of the maxillaries, and entering the mouth between the vomer and 

 the premaxillaries. Head, opercular pieces, and mandibular bones 

 bearing numerous thin bony crests. Eyes large. A single dorsal 

 fin commencing about the middle of the body over against the anal 

 fin, both being continuous. Perfect thoracic ventral fins, with a free 

 bony appendage at the upper angle of their roots. Pseudobranchia 

 present. Branchiostegal membrane with seven rays. No lateral line. 



The small but highly interesting fish upon which this new genus 

 has been established appears to be allied to fishes belonging to genera 

 some of which have been placed by Dr. Giinther amongst the Scom- 

 bridce, others amongst the Carangidce — families distinguished by him 

 on account of differences in the number of the vertebrae. I have 

 been unwilling to open the single specimen obtained with a view to 

 the determination of this point, but place the genus provisionally 

 amongst the Carangidce on account of its many resemblances to An- 

 tigonia. It may be entered in the synopsis of the genera of that 

 family (Cat. Brit. Mas. Coll. p. 418), in sect. /3 of the first group, 

 Carangina, thus : — 



Ventrals with a free bony appendage. 



These appendages, the tooth-like processes of the maxillaries, and 

 the crests about the head present an assemblage of characters quite 

 suflScient to separate this form distinctly from all other known 

 Acanthopterygian genera, 



Diretmus argenteus, sp. n. (PI. XXXVI. fig. 1.) 



D. 27. A. 22. P. IS. V, 10? C. 19. M. B. 7. 



The body is much compressed, and so elevated that without the 

 tail and its fin it is subcircular. The height to the total length is 

 about 1 to 1 f . The abdomen is prominent and keeled, and the nape 

 is trenchant. It is of a silvery-grey colour, with darker grey near 

 the dorsal and anal fins. The skin, when the scales are removed, 

 is fuscous. The whole body is clothed with small, somewhat deci- 

 duous scales, having four or five broad teeth at the edge and some 

 minute spines on the exposed surface. Each scale is constricted at 

 the middle ; the posterior portion is rather larger than the anterior, 



