There are 5 species of Tuditanus thus far known. All of the species are characterized by the possession of a peculiar triangular-shaped clavicle with radiating grooves, and this has been taken as one of the distinctive characters of the genus, as well as of the family. The structure of the cranium where known is quite uniform among the different species. The squamosal is quite large and the supratemporal is not always closely joined to the parietal. The species are: _Tuditanus punctulatus_ Cope, Linton, Ohio. _brevirostris_ Cope, Linton, Ohio. _longipes_ Cope, Linton, Ohio. _minimus_ Moodie, Cannelton, Pennsylvania. _walcotti_ Moodie, Linton, Ohio. =Tuditanus punctulatus Cope.= Cope, Trans. Amer. Phil. Soc., XV, p. 271, 1874. Cope, Geol. Surv. Ohio, II, pt. II, p. 392, pl. xxxiv, fig. I, 1875. Type: Specimen No. 110, American Museum of Natural History, where there is also specimen No. 111. Horizon and locality: Linton, Ohio, Coal Measures. This species, together with the form, _T. brevirostris_, described on p. 88, was used by Cope as the type of the genus _Tuditanus_. Cope subsequently associated some reptilian remains from the Linton mines with the type of _T. punctulatus_ and changed the generic term to _Isodectes_, which was known by another species, _I. megalops_ Cope, from the Permian of Texas. The remains associated by Cope with _I. megalops_ undoubtedly represent a reptilian species and which has been described elsewhere under the name _Eosauravus copei_ Williston. The species is of exceeding interest because it is the _oldest known reptile_ and places the range of the Reptilia down towards the base of the Pennsylvanian. The species _Tuditanus punctulatus_ Cope was founded on well-preserved remains of nearly the entire skeleton of a single individual. The bones are represented by shining carbonaceous matter, and since both of the slabs containing the impression were preserved, a great many characters have been determined. The head, 1 fore-limb, and 23 consecutive vertebræ with ribs are well defined, but of the pelvis and hind limbs nothing is visible. The cranium (fig. 19) is very similar to that of _T. minimus_, from the Cannelton, Pennsylvania, slates. It is triangular in shape, with a narrowed obtuse muzzle. The orbit of the left side is well defined and lies well forward. It is oval in outline and its width is about two-thirds of its length. The nostrils are small and are located well toward the tip of the muzzle. The parietal foramen lies behind the median transverse line which divides the skull equally.