Messrs. Hancock and Attliey on Ctenodus. 259 



under surface ; but a small portion of the scale, exhibiting the 

 upper surface, is adherent, and proves that it is minutely 

 striated in an irregular broken manner, the stride for the most 

 part having a longitudinal disposition. 



The peculiar rectangular form distinguishes these from all 

 the cycloid scales with which we are acquainted ; and they are 

 much thinner than any other of the large scales of the Coal- 

 measure fishes. The only scale that can be compared to 

 them in this respect is that usually attributed to Bhizodus — 

 the scale which we described some time ago as belonging to 

 Archichthys* . But this scale is pretty regularly rounded, is 

 more coarsely granulated on the surface, and usually exhibits 

 concentric lines of growth over the whole surface ; it is also 

 generally found split open, exposing to view the internal 

 structure, when the concentric lines of growth and minute 

 radiating stria3 are sharply defined over the entire surface. 

 The scale of Ctenodus is never seen with the internal structure 

 thus exposed ; at least we have never seen the concentric lines 

 of growth and radiating striae pass beyond the border, the 

 under surface being usually exposed to view. This is well 

 shown in our second species, the specimen being preserved on 

 one slab in relief, the cast of the underside in intaglio on the 

 other. This specimen, too, enables us to judge of the thick- 

 ness of the scale, as it is evident the entire substance of it is 

 present, and that it is not torn open by the splitting of the 

 shale. 



The rectangular outline of these scales we have just pointed 

 out as peculiar ; and in this respect these large scales agree 

 with those we previously described of C. elegans and C. ohli- 

 quHs, the former being the smallest known species of the 

 genus. And here we must not overlook the similarity both 

 in form and size of these large Ctenodus-Bcules to those 

 of the so-called Ceratodus Forsteri^ as figured and described 

 by Dr. A. Gtinther in his valuable memoir on this remarkable 

 Australian fish, recently published in the ' Philosophical Trans- 

 actions.' This resemblance is very striking in our second 

 species, in which the sides are nearly parallel, being a little 

 arched outwards, much in the same way as tliey are in the 

 recent species. In both forms the scales are of an extraordi- 

 nary size : those of Ceratodus Forsteri are two inches and three 

 eighths long, and one inch and six eighths broad ; the largest 

 Cfenof?Ms-scale measures two inches and a half in length, and 

 an inch and a half in breadth ; and that of C. eJegans^ which 

 is quite a small species, is remarkably large for the size of the 

 fish. 



* Anu. Nat. Hist. ser. 4. vol. v. p. 266. 



