STUDIES IN AUSTRALIAN FISHES. 



No. 7.* 



Allan H. MoCdli,ocii, Zoologist, Australian Mnseuni. 

 (Plate.'^ xxi.-xxiv. and Figare 1.) 



Family PLOTOSID^. 



Genus Efiusthmus, (Jiiillnj. 



E>iristhmufi, Ogilbj', Proc. Linn. Soc. N.S.Wales, xxiv., 1, 1899, p. 154 

 (I'lnfdnns eJon<ic(fits, Castelnan). 



This genus is distinguished from Ciiidoijluitls, Giintlier, by the wide 

 isthmus which separates the gill-membi'anes ; its axillaiy poie is also 

 much smaller than that of C. nii'tiastinnnK. 



ECRISTHMUS LEPTDRDS, Gillltlier. 



Long-tailed CatBsh. 



(Plate xxi., fig. 1). 



C)iHlo<ihnn'^ ]rpfurn>^, Giinther, Brit. Mus. Cat. Fish., v., 1864, p. 28. 



D. i/4; P. i/11 ; V. 12. Depth before tlie ventral fins 1:] in tht- 

 length of the head, and 8"5 in the length to the hypural joint; head 6"3 in 

 the same. Head and body 21 in the length of the tail. Eye 307 in its 

 distance from the end of the snout, and 2'3 in the interoculai- space, which 

 is 3-6 in the head. Dorsal spine 2*5, pectoral spine 3-0 in the head. 

 Dorsal fin 21, pectoral fin 1-9, and ventral fin 2-7 in the head. 



General foi-m slender, the tail elongate. Head somewhat depressed, 

 its breadth 1-2 in its length. Nasal barbels about four-fifths as long as 

 the head, and longei- than the maxillary pair. Two pairs of mandibular 

 barbels, the outermost of which are longest. Snout rounded, projecting 

 far beyond the mandible. Lips thick and plicate, the lower forming a 

 free fold near each angle of the mouth which is narrower than the inter- 

 space between them ; posterior angle of the mouth not reaching the 

 vertical of the anterior margin of the eye. Anterior nostril a simple 

 opening near the U[)per lip, the posterior slit-like and 0[)ening on the 

 outer base of the nasal barbel. Surface of the head with numerous minute 

 poies. Preopercular mai'gin completely hidden beneath the skin, tlie opei'- 

 cular edge indicated by a fold. Gill-openings wide but sepai'ated by a 

 broad interspace on the isthmus which is almost as wide as the interocular 

 space. 



* For No. 6, see " Recoi'ds, " xiii., pt. 2, 1920, p. 41. 



