VERTEBRATES. 369 



removed, leaving only the spatulate ridge of the crown, would hardly be sepa- 

 rable from those of D, spatulattts, but as we have teeth of both in nearly per- 

 fect condition, we are compelled to regard them as representatives of allied but 

 really distinct species. 



Formation and locality : Keokuk limestone j Wareaw, Illinois. 



GENUS 3ANDALODUS, N. and W. 

 SANDALODUS CRASSUS, N. and W. 



PI. iv, fig. 3, So. 



TEETH clavate in form, very thick and strong, two inches 

 long, five-eighths inch broad where widest, three-eighths inch 

 thick ; one margin nearly straight, the other forming a broad 

 arch ; crown surface irregularly spatulate in outline, strongly 

 arched in the line of the shorter diameter, toward the narrow 

 end showing a broad but well marked longitudinal furrow ; 

 enamel coating uniformly, rather finely punctate. 



The tooth, of which figures are now given, though from the Lower Carbonifer- 

 ous limestone, is remarkably like those of S. carbonarms, described in vol. 2, 

 p. 104, though by its greater relative thickness, more arched section, etc., spe- 

 cifically distinct. It will be seen that the teeth of these two species present 

 some common characters in their one straight and one arched margins, their 

 broadly rounded anterior end not possessed by the typical species of Sanda- 

 lodus, so that when a larger number of specimens shall be obtained it may be 

 found convenient to divide them into two generic groups. For the present, 

 however, in consideration of the marked similarity which they all exhibit in their 

 surface markings, general spatulate form, longitudinally plane, laterally concave 

 base, it has been thought best to group them together. 



We owe this specimen to the courtesy of Prof. Litton, of St. Louis. 



Formation and locality; St. Louis limestone j St. Louis, Mo. 



GENUS PETRODUS ? McCoy. 

 PETRODUS(?) PUSTULOSUS, N, and W. 



PI. u, fig, 5, 5 ; pi. iii, fig. & 



DERMAL tubercles (?) of large size, very thick and massive, 

 ovoid or sub-triangular in outline, flattened below, arched or 



47 



