358 PALEONTOLOGY OP ILLINOIS. 



Chomatodus paralleltts, St. J. and W. 



PI. X A, Fig. 3, 4. 



The Warsaw beds have furnished a few examples of a form of the 

 above genus which seem to be specifically distinct from the forms indi- 

 cated from the St. Louis, as also those known to occur iu the earlier 

 Keokuk and Burlington deposits, and to which we have applied the 

 above specific designation. 



Teeth of medium or small size, laterally elongated, with the upper 

 and lower margins parallel, moderately thick through the basal margins. 

 Crown symmetrical, more or less compressed and sharp-crested, rounded 

 at the extremities ; the convex face equals in elevation half the entire 

 bight of the tooth, plane or slightly arched vertically, nearly straight 

 laterally, with a narrow coronal belt consisting of two or three imbrica- 

 tions; the concave face is occupied by a rather deep lateral depression, 

 and bordered by three or four well-marked imbricating folds, which are 

 gently curved upward at the extremities where they are confluent with 

 the folds of the opposite face; the crest and basal margins are for the 

 greater extent horizontal and parallel, and in the perfect condition the 

 crown is enveloped in a coating of enamel, which is usually more or 

 less distinctly striated vertically, in worn specimens a coarse punctation 

 appears and the crest presents a more or less jagged outline. The base 

 is thick and strong, nearly perpendicular to the crown, inferior surface 

 relatively wide and obliquely beveled from the concave side to the oppo- 

 site margin, the convex face nearly plane and vertically furrowed, the 

 shallower concave face deeply channeled beneath the produced coronal 

 margin. None of the specimens before us are entire, but some of them 

 plainly indicate a length of three-fourths of an inch, with a hight of 

 .20, elevation of concave face .15, elevation of convex crown face .10. 



The finest example of the above form which has come to our notice 

 was kindly loaned us for description by Dr. G. A. Wiilliams, who 

 obtained it from the Warsaw beds near Boonville, Mo. It is related 

 most intimately with that described from the St. Louis limestone under 

 the name G. incrassatus ; but, at the same time, its less robust propor- 

 tions, more symmetrical form, parallel margins, less angular basal 

 extremities, and greater inequality in the elevation of the respective 

 coronal faces, will readily serve to distinguish it from the latter form. 

 Authentic specimens are known to occur only in the Warsaw beds, 

 where it has been found on the Piasa, above Alton, while in the St. 

 Louis limestone in the same region its presence has not been detected, 

 although these deposits have been most thoroughly studied by Mr. VAN 



