4 FISH OF THE CARBONIFEROUS PERIOD. 



a slight backward curve ; about one-fifth of the surface towards 

 the apex perfectly smooth ; the remainder, under the lens, is 

 minutely and irregularly striated longitudinally. 

 This remarkable tooth, the only species I as yet know of the 

 genus, seems to present all the characters, external and micro- 

 scopic, of a true Saurian reptile ; and when we compare it with 

 Herman von Meyer's genus Pistosaurus, for instance, of the 

 Laineckerberg Muschelkalk and other allied Saurians, the resem- 

 blance is such as to caution geologists against laying too much 

 stress on the supposed first appearance of reptiles in the mag- 

 nesian limestone, when drawing a line which would separate this 

 group from the palaeozoic rocks below^ 



Common in the bituminous carboniferous shale of Carluke, 

 Lanarkshire. 



[Col. Cambridge University.) 



Colonodus (M'Coy), n. g. 

 (Etym. Koikov, ilia, and ohov^, dens.) 

 Gen. Char. Tooth elongate-conic, very gradually tapering, sec- 

 tion round near the base, becoming trigonal towards the apex ; 

 front even, sides impressed with short, alternating, transverse, 

 wrinkle- like furrows ; enamel-like surface smooth, highly 

 polished, longitudinally marked with few, distant, minute im- 

 pressed striae ; it terminates obliquely at the base, the edge 

 being slightly notched or wrinkled ; base forming a short, 

 slightly dilated round disc, placed obliquely to the axis of the 

 tooth, and extending farther behind than in front, truncated 

 below and of a coarse osseous texture : medullary cavity about 

 one-third the diameter of the tooth, cylindrical, from which, 

 under the microscope, the flexuous, distant calcigerous tubes 

 are seen to radiate directly to the surface, towards which they 

 become gradually finer and closer. 



This tooth is not unlike a bit of small intestine tied at the end, 

 being nearly cylindrical, smooth, glossy, and slightly wrinkled 

 transversely along the sides. In general external character it 

 approaches most to Dendrodus and Rhizodus, but is destitute of 

 the longitudinal flutings towards the base, which are so intimately 

 connected with the internal structure of those teeth ; the trans- 

 verse wrinkling of the sides is also a strong external difierence. 

 The fine longitudinal scratch-like strise of the surface resemble 

 what we see in the enamel of Suchosaurus, &c. It is its internal 

 microscopic structure which most perfectly distinguishes it from 

 its allies, for by its simplicity it is at once widely removed from 

 Dendrodus ; and from Rhizodus, which it most nearly approaches 

 in structure, it is distinguished (besides the differences in ex- 



