316 PALAEONTOLOGY OF ILLINOIS. 



and which do not appear to be referable to the dentary system. These 

 bodies are exceedingly small, irregularly circular in outline, with a 

 depressed convex coronal portion which rises into an eccentric acumi- 

 nation or transverse ridge along one side, and delicately sculptured with 

 irregular carinas radiating from the apex towards the marginal borders. 

 The base is sometimes slightly produced opposite the abrupt face in a 

 thin border, and more or less concave below. There is great diversity 

 of form, no two specimens presenting precisely the same shape, though 

 all partaking in a general resemblance, and especially in the dark, horny 

 lustre of the enameled crown, by which they are readily distinguishable 

 from the teeth with which they arc associated. It seems not improbable 

 that these minute bodies constituted part of the dermal or shagreen 

 covering of the fish. One of the better preserved of the scales is shown 

 in fig. 21, PI. 8. Often the long slope of the crown exhibits greater or 

 less indications of abrasion in the smooth surface it shows, aud which 

 may indicate the relative position of the anterior and posterior sides. 



Neither of the remarkable suites of fossils noticed above furnish any 

 clue to the nature of the dorsal fin defenses, if with such these fishes 

 were provided. Eemains of the firmer cartilages occur, which probably 

 belonged to the supports upon which the teeth rested. These fragments 

 are of variable thickness, portions from the dentary ridge of the jaw 

 attaining a thickness of .40 inch, while fragments of what may have 

 constituted the inner-fold or other less exposed walls of the jaw, are of 

 extreme thinness, sometimes not more .05 inch in thickness. These 

 masses appear to be composed, in the one case of an aggregation of 

 semi ossified particles, aud in the latter of similar points presenting an 

 elongated polygonal outline; the sutures between the hard parts are 

 often filled by mineral matter, giving to the mass a minute reticulated 

 or honey-combed appearance when the substance of the partially ossi- 

 fied tissue has been dissolved away. 



The present group of teeth was first brought to notice by the investi- 

 gations of Messrs. Newberry and Worthen, published in 1870, in 

 the preceding fourth volume of this Report, where it is designated under 

 the generic name Lo2)hodus. This term having been previously employed 

 by Col. Rohanowsey to designate a group of. teeth from the Lower 

 Carboniferous formations of Russia, aud which are also common in the 

 same deposits in Great Britain and America, it is obvious that the above 

 name must give way. 



In the above mentioned volume, two species were described uuder 

 the names L. variabilis, from the Upper Coal Measures near La Salle, and 

 Orodus corrugatus, from the Lower Coal Measures near Alton, in this 

 State. The latter, as suggested by Messrs. Newberry and Worthen, 

 is unquestionably generically allied to the teeth described under the 



