158 DR. RICHARDSON'S DESCRIPTION OF AUSTRALIAN FISH. 



Dimensions. 



In. Lin. 



Length from edge of upper jaw to tip of the caudal 17 1 



Length from edge of upper jaw to beginning of anal 7 7^ 



Length from edge of upper jaw to centre of anus 7 6 



Length from edge of upper jaw to beginning of dorsal 7 5^ 



Length from edge of upper jaw to branchial sUt, or pectoral ... 21^ 



Length from edge of upper jaw to angle of mouth 7^ 



Length from edge of upper jaw to centre of the eye 5^ 



Length of projection of lower jaw beyond the upper (mouth open) . 1^ 



Breadth between the tubular nostrils 3^ 



Length of the pectorals 65 



Height of vertical fins 2f 



Height of occiput 10 



Height of body 9 J 



Thickness of body 



OsTRACioN LENTicuLARis (Noh.), Lenticular Trunk-fish. — Ostracionlenticularis, Richard- 

 son, Zool. Proceed. March 9, 1841. 



Os. inermis, ovalis, compressus, dorso ventreque carinatis. 

 I am indebted to Dr. Andrew Smith for the liberty of describing two specimens of an 

 Australian Trunk-fish, which are highly interesting as exhibiting a modification of form 

 which has not been hitherto noticed to exist in this singular genus. In general structure 

 this new species approaches most nearly to the sub-generic group characterized by 

 J. E. Gray, Esq. under the appellation of ' Aracana.' The Chinese Aracana reevesii of 

 that author has a keeled back, and thus forms a link between the more common Van 

 Diemen's Land Aracana, which have convex backs, more or less broad, and the lenti- 

 cular form of the species at present under consideration. Dr. Smith's two specimens 

 are evidently examples of one species at very different ages, and the epidermis having 

 been mostly worn off" them, scarcely any traces of the original colours remain. I re- 

 ceived no account of their habits, but as the smallness of their fins and the strength 

 and elasticity of their cuirass fit them for being tumbled about in the surf of a rocky 

 coast, it is probable that, hke the other Trunk-fish, they inhabit such places. 



Form. — Much compressed, the greatest thickness measuring less than half the height. 

 The profile of the body is an almost regular ellipse, whose transverse axis exceeds the 

 vertical one by about one-fourth. The sides are convex and meet in acute mesial keels 

 on the back and belly. The dorsal keel commences a little posterior to the pectorals, 

 the nape being obtusely rounded and the space between the orbits nearly flat, or in the 

 older specimen slightly concave, from the greater projection of the borders of the orbits. 

 The general stnicture of the cuirass and the disposition of its parts is the same as in the 

 Aracana. A slight degree of motion is permitted by a membranous line which extends 

 from the angle of the lips to the branchial slit, and the cuirass is truncated posterioriy 



