1856.] '^9 



RHIZODUS Owen. 



R. LANCiFER Newb. Teeth striated below. Section elliptical, smooth toward 

 ithe summit, where they are very much compressed, with a lenticular sectiom 

 and cutting edge on both sides. Form of summit of tooth like that of a lance 

 head. Near the apex of the tooth the cutting edge of one side is slightly gib- 

 bous, an apparent tendency toward a barbing o/ the point, as in some species 

 of Lcpidosteus. 

 ^ As usually found, the plicated base of the tooth has mostly disappeared, the 

 solid point alone remaining ; this is about an inch in length. The entire tooth 

 was more than twice that length. 



R. iNCURYDS Newb. Head massive. Superficial bones strongly tuberculated. 

 Tubercles elongated, vermicular, sometimes becoming elevated lines of a line in 

 breadth, and having a radiated arrangement. Jaws strong, both thickly set 

 .with strong ancipital curved teeth. These teeth are striated below, ellipti- 

 cal in section, and toward the summit curved backward toward the throat. They 

 are of difi'erent sizes, as in all allied fishes. The smaller teeth are G to 9 lines in 

 length and thickly set; the larger ones are much fewer in number, and more 

 than twice as long. One of the larger teeth is placed near the extremity of the 

 lower dentary bone of each side, as in R. gracilis McCoy. 



E. ANGUSTCS Newb. Laniary teeth elongatied, slender, finely striated at base, 

 smooth above, with cutting edges. Subordinate teeth half the length of the 

 larger ones. Conical, acute, striated at base, with a circular section throughout. 

 Surface of jaw coarsely tubercled. 



In this diversity of form in the teeth, this species differs from R. gracilis 

 McCoy and from R. Mibbcrii Ag., as well as from the. other species I have found 

 in Ohio. In R. incurvus N., however, the teeth have a section so nearly circular 

 Xhat there seems no good reason for separating them ;by generic distinctions. 



Of all the species of Rhizodus, which I have found, I probably have scales and 

 perhaps vertebrae and cranial plates, but as yet have been unable to find these 

 organs connected with the teeth. 



DIPLODUS Agass. 



D. coMPRESsus Newb. Teeth of moderate size, base small. Lateral denticles 

 unequally spreading, compressed, with acute points and strongly crenulated 

 edges. Central denticle very small, acute, compressed, finely crenulated on 

 margin, 



D. GRACILIS Newb. Tooth as large as D. gibboaus Agass. Base very small. 

 Lateral denticles long, curved, slender, divergent towards the points, much less 

 compressed than in preceding species, less acute, and less conspicuously crenu- 

 Sate on margins. Median denticle small, subulate, scarcely ci;enulate on margins. 



D. LATUS Newb. Teeth very large and very robust. Lateral denticles neariy 

 straight, and on the same plane, divergent, ^ to k as broad at base as long, 

 .compressed. Each margin strongly crenulated. Middle cone obsolete, or re- 

 duced to a simple knob. Base of tooth large, under surface flat. 



Ail the specimens of Diplodus from Ohio which have come under my observa- 

 tion, ntmbering some hundreds, have crenulated margins, in that respect pre- 

 :Senting a striking difference from the species described by Agassiz. 



CLADODUS Agass. 



C. acumjNatus Newb. Central denticle elongated, conical, acute ; lateral 

 denticles very acute, compressed. Base small and thin. 



CHIRODUS McCoy. 



C. ACUTUS Newb. Teeth as long as C. pes-ranx McCoj, hut more slender 

 nhraughauL Denticles more .acute^ 



