Dr. R. H. Traquair on Harpacanthus. 



495 



very well grasped by him in his definition of Tristi/chius, and 

 he lays particular stress upon the presence of the three long 

 ridges, on which he in fact founded his generic name. But if 

 we compare Agassiz's figure of T. arcuatus with that of Mr. 

 Stock^s ^^Tristi/cJiius^^ Jimh'iatiis, it will be apparent that the 

 two forms have hardly that amount of resemblance which would 

 warrant reference to a common genus. Agassiz's Tristychius 

 is eminently ridged and striated — Mr. Stock's spine is per- 

 fectly smooth. The former is gently curved and tapering, 

 and shaped generally like tlie spine of Hyhodus ; the latter 

 is nearly as thick at the extremity as at the middle, and 

 shows, moreover, a very peculiar sudden backward curve. 

 To this curve Mr. Stock attaches " very slight importance," 



Fi- 1. 



Fig. 1. — Harpacanthus fmhriatus, .Stock, sp. Here the greater part of 



the spme is seen only in impression. 

 Fig. 2. — The other side or counterpart of the same specimen, containing 



more of the actual spine, but wanting the impression of the distal 



extremity, which has splintered off. 



remarking also that it is " possibly due to disease ; " and he 

 has also given a " restoration " of the spine, in which he has 

 to a large extent straightened it out, so as to make it look 

 rather more like that of the genus in which he has placed it. 

 A second specimen of the same spine has, however, subse- 

 quently been found in the same locality by Mr. W. Anderson, 

 now of the Geological Survey of New South Wales, to whom, 

 along with Mr. W. Tait Kinnear, the discovery of the first 



