Cope, Proc. Am. Phil. Soc., XXII, p. 407, 1885.
Cope, Proc. Am. Phil. Soc., XXXVI, p. 85, pl. iii, fig. 2, 1897.
Moodie, Proc. U. S. Nat. Mus., vol. 37, p. 23, 1909.
Type: Specimen in the American Museum of Natural History. There are also specimens Nos. 4472 and 4473 in the U. S. National Museum.
Locality and horizon: Linton, Ohio, Coal Measures.
The species was founded on a complete skull preserved on obverse sides of a block of coal. Cope ([123, pl. XLII, fig. 2]) figured this skull. The figure is poorly executed and does not do justice to the specimen, which is really well preserved. In general the skull is oval, with the orbits located well towards the acuminate snout. The interorbital space is equal to twice the width of the orbit. The pineal foramen lies near the center of the skull. The quadrate angles are drawn out into slender acuminate, longitudinally striate horns, processes from the squamosal. The "horn" arises from an expanded base, which is a portion of the cranial element at the postero-lateral angle of the skull. This character is taken as the distinctive one of the genus. It is possessed by no other form of Carboniferous air-breathing vertebrate, in association with the other characters of the form.
The boundaries of the premaxillæ are indefinite, but what remains of the sutures indicates that the elements were small. No teeth have been detected. The nasal is likewise not clearly defined, but the frontal is an elongate element which occupies the space between the orbits and joins the parietal posteriorly. The parietals form a large oval space, so characteristic of many of the Carboniferous Microsauria, in the anterior third of which occurs the median parietal foramen. The postparietal is almost square, and forms part of the posterior boundary of the skull. The tabulare has the usual position and relations. The prefrontal is ill defined. The postfrontal is small and forms a slender rod on the postero-inner boundary of the orbit. The postorbital is small and its bounding suture with the postfrontal is indefinite. The jugal is only partially represented in the specimen, and that part forms the outer boundary of the orbit. The maxillary sutures are not defined. There are no evidences of teeth, since the skull is compressed dorso-ventrally. The quadratojugal is, apparently, a larger element than usual, with the visual relations. The supratemporal lies in great part in front of the squamosal, but still has the normal relations of that element. The squamosal is the characteristic feature of the skull. It is very tumid at its base and projects into a long, slender, acuminate horn, the tumid portion being ornamented by radiating striæ.
Another specimen of this species presents the greater part of the skeleton. However, very little can be added to our knowledge of the skull structure. It is barely possible that the second specimen may be distinct from the type. The horns are curved inward, but otherwise there is little or no difference. One of the most interesting and important features of the complete specimen is the unusual preservation of a leg, with impressions of 15 or more vertebra;, and traces of curved ribs which are intercentral in position.
The femur is slender and expanded at the ends, with the articular surfaces well formed. The tibia and fibula are mere rods of bone, although the tibia has slightly expanded extremities. There is no osseous tarsus. There are 5 digits in the foot; the second one is entire and contains 4 phalanges; the other digits are incomplete. The foot is remarkably long and slender, and is fully as long as the tarsal space plus the tibia, with the terminal phalanx clawed.