272 Proceedings of the Royal Society of Victoria. 



Description. — According to Professor Tate, this " species is 

 somewhat comparable with S. magnus, Agassiz, but is narrower 

 with coarser reticulate rugosities and the inner margin is very 

 finely reticulate-punctate ; the outline is subtrapezoidal, about 

 three times as long as wide, broader at one end, which is con- 

 vexedly truncate and narrower at the other, which is trun- 

 cated ; uniformly depressedly convex above." This differs 

 from Cestracion, amongst other points, in having a distinct 

 articulating keel entirely round the tooth instead of on the 

 outer side, and in the absence of the narrow submedian band 

 on the upper surface. In the microscopical structure of the 

 teeth there is also definite evidence of the affinity of this form 

 with Asteracanthus, for in a vertical section the tubuli in the 

 dentine layer are arranged in close more or less parallel bundles 

 and quite distinctive from the structure seen in the teeth of 

 Cestracion. 



Dimensions. — Small specimen — Length, 17 mm.; breadth, 6.5 

 mm.; height, 2.5 mm. 



Medium specimen — Length, 29 niui.; breadth, 11.5 mm.; 

 height, S mm. 



Large specimen — Length, 32.5 mm.; breadth, 11.5 ram.; 

 height, 8.5 mm. 



Locality and Horizon. — Geological Survey, T.M. 2. Lime- 

 stone of the Moorabool Valley near Maude. Professor Tate's 

 figured specimen is recorded as from Cheltenham, Port Phillip, 

 i.e., Beaumaris. He also mentions its occurrence in "Lower 

 Murravian," and refers to a specimen in Mr. Sweet's collection 

 from the limestones of the Moorabool River. ^ 



Observations. — The teeth of Asteracanthus are decidedly 

 rarer in our Cainozoic Beds than Cestracion, but, judging from 

 Professor Tate's remark, " fi8h-23lates, which are not of uncom- 

 mon occurrence at Cheltenham," he appears to have included 

 Cestracion as referable to Strophodus. Strophodus, however, 

 has been displaced in favour of Asteracanthus, and is now re- 

 garded as a synonym. The structure of the teeth of the above 

 species is very distinct from that of Cestracion, as will be seen 

 from the photograph, PI. XIL, Fig. L 



This specimen has been since presented to the National Museum by Mr. Sweet. 



