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NOTES ON THE DISCOVERY OF A GANOID FISH 



IN THE KNOCKLOFTY SANDSTONES, HOBART. 



Bt Messrs. R. M. Johnston and A. Morton. 



Two Plates. 



Tlie recent discovery of the very perfect remains of a 

 Ganoid Pisli, ciosely allied to the genus Acrolepis, in one of 

 the beds of the Knocklofty sandstones, is of the greatest 

 interest. Several fossil fishes are said to have been found 

 previously in the flagstone quarry near the Cascades, but, 

 unfortunately, the quarrymen regarded them as being of 

 little or no importance, and although, from curiosity, one or 

 two specimens had been preserved for a time by one of the 

 workmen, they were soon lost or thrown away. The specimen 

 now referred to was discovered by Mr. H. Nicholls, who, 

 with commendable thoughtfulness, at once presented it to 

 the Tasmanian Museum. 



Fortunately the casts of the specimen are remarkably 

 perfect. The only parts imperfect, or missing, are the ventral 

 fins, part of the anal fin, and the anterior part of the head. 

 The strongly pronounced heterocercal tail and the scales of 

 the body are remarkably well preserved. The following is 

 a description of the fish, which is named, provisionally, in 

 honour of His Excellency Sir Robert Hamilton, to whom, as 

 its President, the Royal Society is so much indebted for the 

 enthusiastic manner in which he has ever promoted its 

 interests. 



Acrolepis ? Hamtltoni, Johnston and Morton. 

 Body compressed, elliptical, elongate ; length from snout to 

 end of caudal fin about 7 inches ; length of body 5| inches ; 

 depth at a vertical line through occiput, 12 lines, increasing 

 to 14 lines at greatest depth near ventrals, and from thence 

 gradually tapering to peduncle, where it measures 5 lines ; 

 length of heterocercal tail — which is inclined upwards at an 

 angle of about 22 degrees — 14 lines ; length of lower ray 

 lobe of caudal, 5 lines ; length of head about Ij inches, or 

 scarcely one-sixth of the total length; length of dorsal, 

 about 8 lines; fin low, with fine rays, probably 15 or 16; 

 anterior end situated about 39 lines from end of caudal, and 

 the posterior distant about 31 lines from the same point. 

 The anal fin is inconspicuous and imperfectly preserved, but 

 it appears to be similar to the dorsal, and it is situated fully 

 half the length of that fin nearer the tail. The ventrals are 



