160 DR. RICHARDSON'S DESCRIPTION OF AUSTRALIAN FISH. 



In. Lin. 

 Length from upper lip to centre of orbit 14 



Diameter of orbit 7 



Height of dorsal Oil 



Height of anal 9^ 



Length of caudal lobes 1 3| 



Length of central rays of caudal 1 1 



Greatest vertical height of body 3 6^ 



Greatest thickness of body 17 



OsTRACiON AURiTus (Shaw), Shaw's Sea-pig. 



Tab. IX. Figs. 1 and 2. 



Os. (Aracana) ventre pallente unicolore; lateribus dorsoque lineis saturatis, rectis et 

 curvis ornatis, quorum qinnque sub oculo et tribus in basibus pinnarum verticalium. 



This Trunk-fish, known locally like the other Australian species by the name of ' Sea- 

 pig,' belongs to a section of the genus which has been named ' Aracana' by Mr. Gray. 

 In the ' Magazine of Zoology and Botany' for 1838 (p. 108), that gentleman describes 

 five species of Aracana, viz. four from Van Diemen's Land, and one from the China 

 seas. On an attentive examination of Shaw's original specimen of his Ostracion au- 

 ritus with seven others, all in the British Museum (numbered from 39 to 47 inclusive), 

 and with three of very different sizes sent from Port Arthur by Mr. Lempriere, I am 

 inclined to believe that the species varies considerably with age, that the Aracana lineata 

 (Gray) is the younger individual, and that the 0. striatus of Shaw, of which I have seen 

 no example, is not perhaps distinct. 



In Aracana a section of the body is bounded by five flatly curved lines, the lateral 

 ones being curved and meeting the back nearly at right angles, but the two lower ones 

 which define the belly being inclined towards each other in an obtuse angle and forming 

 at their junction a ventral keel, more or less prominent and obtuse, according to the age 

 of the fish. The relative proportions of the sides to each other vary with the species, and 

 in a lesser degree with age also. There are three strong bony spines at the junction of 

 the back and side, the anterior one rising from the margin of the orbit, and three at the 

 junction of the belly and side, the anterior one being nearly under the branchial slit. 

 There is a seventh spine behind and above the level of the pectoral on the middle of the 

 side, making with those on the other side of the fish fourteen in all. The number is 

 not invariable, some of the inferior spines being occasionally absent in young specimens, 

 and there is sometimes an additional one in the upper or under row, or in both. In 

 the young the spines are for the most part more conical and pointed, and as they in- 

 crease in length they become at the same time broader, thinner, and more curved. 



The structure of the cuirass is essentially the same as in Ostracion lenticularis de- 

 scribed above, but in the recent fish the epidermis conceals the limits of the plates, 

 though the radiating lines of small grains which divide by their intersections the whole 



