Type: It is impossible to determine which one of the specimens is the type. There are numerous representatives of the species, as follows: Nos. 140, 1096 G, 8345 G, 8555 G, 1089 G, 2, 132, 133, no number, 1094 G, 8545 G, 8677 G, 1159 G, 105, no number, 1091 G, 7a, 1092 G, 1093 G, 1095 G, 153, and others unnumbered in the American Museum of Natural History; in the U. S. National Museum are the following: Nos. 4458, 4463, 4464, 4514. ([Plate 20, fig. 2.])
Horizon and locality: Linton, Ohio, Coal Measures.
The most abundant species of the Linton Coal Measures. There are over three dozen specimens preserved in the Newberry collection. The species is a clearly marked one, as a rule, though there is great variation in the size of the body and the form of the vertebræ. Though there are several apparently complete skulls preserved in the collection, it is impossible to make out the morphology of the elements on account of the amount of crushing to which the skulls have been subjected.
Fig. 30. Restoration of Ptyonius. × 1.
The head is lancet-shaped, and the muzzle very elongate, slender, and acute at the extremity. The head is in fact a miniature of an ichthyosaur cranium. ([Plate 20, fig. 2.]) The orbits are large and posterior to the median line. The anterior portion of the skull is narrow, posteriorly truncate, and the mandibular angle is projecting. The posterior portion of the mandible is sculptured. Possibly the entire cranium was also, and this has been lost; in fact, this sculpturing is indicated in one or two specimens. The teeth are conical and sharp, longitudinally striate, and anisodont. There seems to be evidence of palatine or pterygoid teeth, though this needs confirmation. The pectoral plates are well preserved, with the interclavicle a narrow oval, with anterior and posterior prolongations. In one specimen it is sculptured. The clavicles are narrow and slightly sculptured. The abdominal scutellæ are bristle-like.
The vertebræ are short, with expanded neural and hæmal spines. The expanded condition of the neural spines begins over the thoracic region, where they are low. They become well developed in the posterior dorsal region. The caudal fan-shaped spines are larger. The dilated portions form equilateral triangles which stand on moderately short pedicels. They are weakly ridged, and each ridge is prolonged into a narrow acute tooth beyond the margin, 11 of which may be counted on one of the best preserved spines. The longitudinal striæ are terminated near the pedicel by two others which cross obliquely from each side, and, meeting, present the appearance of the margin of a cup sculptured in relief, from which the striæ arise. Pedicels smooth. The spines are in contact at their angles, thus forming a continuous line. In a typical specimen there are 6 in half an inch, in another 7, and in a third 8. The ribs are well-developed and slender.