THE MICROSAURIAN FAMILY STEGOPIDÆ, FROM THE COAL MEASURES OF OHIO.

Family STEGOPIDÆ Moodie, 1909.

The chief family characters are the large lacrimal, unknown in other species of Coal Measures Amphibia, the central position of the orbits, the general form of the skull, and the peculiar, short, divaricate horns from the squamosal. If an intertemporal element is present in the skull, which is suggested as a possibility, the family is further distinct. The type species is Stegops divaricata Cope from the Linton, Ohio, Coal Measures.

The group seems to be distinct and has no immediate allies, being confined to the American Coal Measures.

Genus STEGOPS Moodie, 1909.

Type: Stegops divaricata Cope.

This genus has been erected for the reception of the peculiar form described by Cope as Ceraterpeton divaricatum, but there are good reasons why the form can not be retained in the genus. The position of the orbits in Stegops (plate 25, fig. 3) is different from Ceraterpeton and the muzzle is rounded, not truncate as in the latter form. The horns are of a different type and there is no indication of the tabulare protuberance which is present in Ceraterpeton. The sculpturing of the cranial elements is also distinctive in the present form, consisting of radiating grooves and ridges; the cranium of Ceraterpeton appears to be but slightly sculptured. There is no lateral projection from the border of the skull in Stegops, as there is in the other genus. The structure of the skull of Ceraterpeton is practically unknown, except in a very general way, although Andrews (8) was able to make out some of the elements and to trace the lateral-line canals. A structural comparison is thus impossible, but on the basis of form alone there are good generic distinctions. The present genus is apparently distinct from other genera in the presence of an intertemporal, but additional material will be required before a satisfactory determination is possible. The genus Diceratosaurus of Jaekel (347) is distinct in the arrangement of the elements of the cranium, the general form of the skull, and in the two known species of Diceratosaurus the orbits are located well anteriorly, but in Stegops they are in the median transverse line of the cranium. The genus Stegops is distinct from Eoserpeton in the smaller size of the prosquamosal, in the broadly rounded muzzle, in the larger and more posteriorly placed orbits, and in the presence of an intertemporal bone, or at least in the elongate character of the postorbital if the intertemporal is not present. The species on which the genus Eoserpeton is based was first described by Cope as Ceraterpeton ten n iconic. The form is quite distinct, in spite of Jacket's protestations to the contrary. The genus Stegops stands alone among the Carboniferous Amphibia of North America, so far as I am aware, in the possession of a well-defined lacrimal of the labyrinthodont type.

Stegops divaricata Cope.

Type: Specimen No. 2559 G, American Museum of Natural History. The obverse of this is No. 12,311, Walker Museum, University of Chicago.

Horizon and locality: Linton, Ohio, Coal Measures.

The skull on which this species is based consists of the impressions on two slabs of coal, one belonging to the Newberry Collection of the American Museum of Natural History, No. 2559 G, and the other to the Gurley Collection of the University of Chicago, No. 12,311. The slab belonging to the University of Chicago contains the better-preserved remains, so that the description is based largely on that portion (plate 25, fig. 3). Nearly all of the elements of the skull are determined with considerable certainty and many important characters in the morphology of the Microsauria are thus brought out.

The skull is oval, elongate, truncate behind, and the quadrate angles project into sharp horns. The orbits are elongate ovals and their center lies in the median line which divides the skull transversely. The nostrils are elongate and have an oblique position. The pineal foramen lies in the posterior third of the skull.

Teeth are preserved on both maxillÆ and premaxillÆ. They are simply sharp pleurodont denticles, and seem to have been fairly abundant. The bones have been completely carbonized and nothing of the original texture is preserved, although the details of the structure are beautifully preserved. (PLATE 25, fig. 3.)

The skull is somewhat triangular in its general form. The premaxilla lies on the anterior border of the cranium, and forms the median border of the nostril. The suture which separates the maxilla and the premaxilla is not evident, and it may not be correctly defined in the figure (fig. 23). The nasal is a very large element and is elongate. It unites with the premaxilla, the lacrimal, the prefrontal, and the parietal. It is acuminate behind and the point is inclosed by the pref rental and the parietal. The frontal is quite narrow and elongate, and does not border the orbit; its posterior boundary is not accurately represented. The radiations on the surface indicate the extent of the element. The parietals are remarkable in being smaller than the frontal and nasal. The pineal foramen is inclosed in the median suture in the anterior third of the parietals. The parietal has the usual relations of that element. The postparietal lies posterior to the parietal, but a portion of its bounding sutures are destroyed. The prefrontal forms the antero-interior border of the orbit and borders the postfrontal posteriorly, in an unusual manner. The lacrimal is a large element and is clearly separable from the other cranial elements. It, with the prefrontal, forms the anterior border of the orbit. The maxilla is very elongate and forms the larger part of the lateral border of the skull. Sharp-pointed teeth are present on it and they may have been pleurodont. The lateral border of the orbit probably received a portion of the maxilla. The postfrontal and the postorbital form the greater part of the posterior boundary of the orbit. The postorbital seems to be divided by a median suture which would indicate an intertemporal bone, but this is not certain. The appearance may be due to a fracture. The supratemporal is a large element bordering the parietal and lies in front of the tabulare. The squamosal is elongate to form the posterior horn-like extension of the skull. The tabulare is transversely elongate and has the usual relations. The jugal widens to a fan-shape backwards, and helps to form the lateral border of the orbit. Its lateral and anterior boundaries are not assured. The quadratojugal seems to lie as indicated, although the anterior part of the suture is not distinct. It is apparently an elongate element and with the maxilla forms the lateral border of the skull. The base of the skull as restored (fig. 23) is irregular and may have had a slightly different form.

The genus Stegops is exceptional in the elongate character of the cranial elements of the single species known. In this respect it recalls the species Diceratosaurus lÆvis described below. The large size of the nasals, frontals, and lacrimals and the small size of the parietals are, so far as I am aware, unparalleled among the other Coal Measures Amphibia of North America.