90 PALAEONTOLOGY OF ILLINOIS. 



Teeth. — The group of teeth here impacted together, includes at least four 

 distinct and different forms, of which the surface markings, microscopic struc- 

 ture, color, etc., are precisely the same throughout. These are, first, large, 

 strongly enrolled teeth, marked with two strong, revolving ridges, separated by * 

 a deep furrow (figs. 3 and 4, pi. VII), which correspond to the larger of the 

 two teeth of either ramus of the jaw, figured by Prof. Agassiz, (Poiss. Foss. 

 Adas, tab. 19, fig. 14,) constituting the type of the genus Cochliodus, and the 

 tooth described by Prof. McCoy under the name of 0. acutus, Ag., (Brit. 

 Palseoz. Foss. p. 621, pi. 3 i, figs. 24, 25). The differences between these teeth 

 and ours being only of a specific character. Our specimens are three times as 

 large as those of Agassiz, the broader ridge terminating in a rounded promi- 

 nence before reaching the margin; the surface of the tooth strongly wrinkled, 

 etc. These teeth are regarded by McCoy as the posterior pair of the lower 

 jaw. 2d. A narrow tooth equally convoluted, having a wedge-shaped outline 

 when seen from above; perhaps corresponding to the anterior pair in Agassiz's 

 figure. This tooth has a single narrow and low revolving ridge, with numerous 

 obscure plications. 3d. Teeth nearly as long as both the preceding, (figs. 1 

 and 2, pi. VII), with one broad, rounded, revolving ridge near the oblique 

 extremity, with one or two low and narrow ones near the opposite end, and 

 numerous revolving wrinkles or folds upon the intermediate surface. These 

 teeth are somewhat unlike any heretofore attributed to Cochliodus, and proba- 

 bly belonged to the opposite jaw from that which bore those before mentioned; 

 matching into those when in use. If the teeth described by Agassiz and 

 McCoy are, as supposed, from the lower jaw, these are from the upper. 4th. 

 Transversely elongated teeth of smaller size, in diminishing series of six, 

 joined by their longer sides, and in some cases retaining their relative positions. 

 (PI. VI.) These teeth have more or less distinctly marked prominence or 

 cone upon the crown, and oblique and flattened root often as high as the crown. 

 Considered by themselves they would constitute one or more typical species of 

 the genus Helodus. They formed several rows, as is indicated by the differ- 

 ences which they present. In one series taken from this group (fig. 5, 5 a, 

 PI. VI,) the cone of the crown is more or less mammillary in form, sub-central 

 in position, the lateral extremities of the teeth rounded. In another series 

 from the same mass, (PI. VI, fig. 4, 4 a), the cone of the crown is more flat- 

 tened and very eccentric, the lateral extremities obliquely truncated. A third 

 series consists of six (6) small, elliptical teeth, of which the crowns are arched 

 over without distinct cones. (Fig. 6, PI. VI.) 



The enameled surface of all these teeth, large and small, has a relatively 

 coarse porosity precisely the same in all, and it is impossible to resist the con- 

 clusion that they all formed parts of the varied dentition of a single fish. As 

 they are now thrown into a confused heap we can only conjecture what the 



