VERTEBRATES. 303 



truncated or broadly rounded, strongly constricted basally, traversed 

 by a low, undulated, obscurely defined median crest, 'which bears at 

 irregular and infrequent intervals obtuse, or nearly obsolete, secondary 

 prominences, from which descend obscure plicse, which bifurcate below, 

 forming numerous vertical ribs in the region of the basal margins ; the 

 median prominence, as well as the lateral crests, is smooth, only the 

 middle and basal portions of the crown are distinctly costate, the rela- 

 tively narrower anterior surface is even less strongly folded, and the 

 entire coronal surface is regularly and minutely punctate. Greatest 

 diameter of medium-sized tooth about two inches, greatest bight of tooth 

 .95, antero-posterior diameter at base of median cone .70, breadth of 

 lateral wings .43, greatest hight of crown .50, elevation near the extremi- 

 ties .IS; greatest thickness of root .40 inch. Other examples attain 

 above three inches in length. 



The above species, of which we have examined but three or four 

 representatives in the collections of Messrs. Springer and Wachsmttth, 

 is one of the largest and finest of the genus, and the interest which 

 attaches to these specimens is further enhanced by the fact that they are 

 among the very few examples of ichthyic remains which the researches 

 of the above gentlemen have brought to light in the Lower Burlington 

 limestone. The specimens unfortunately are not perfect, although their 

 state of preservation is such as to enable their form and superficial 

 characteristics to be quite fully determined. The coronal region bears 

 unmistakable signs of abrasion, by which the vertical rugae have been 

 obliterated in the region of the crest, and consequently obscured in the 

 basal portions ; but their general form and direction is still discernible, 

 and aid in the determination of the characteristics by which the form 

 is especially distinguished in the absence of the enamel layer and any 

 delicate markings it may have preserved. 



These teeth have only remotely intimate resemblances with any of 

 the numerous species of Orodus now known, bearing, perhaps, as close 

 resemblance to 0. ramosus, Agass., as to any of its congeners from 

 American localities. It has little in common, save the uniformly punc- 

 tate condition of the abraded coronal surface, with the form so numer- 

 ously represented in the Upper Burlington fish-bed, to which we have 

 applied the name 0. variocostatus, the costse being less widely and 

 irregularly spaced, and the median prominence less prominently pro- 

 duced. 



Position and locality : Rare in the Lower Burlington limestone ; Bur- 

 lington, Iowa. 



