This species was first described by Newberry as a fish belonging to the genus _Pygopterus_. Cope later placed it under the genus _Colosteus_ and clearly showed its amphibian characters. The genus _Colosteus_ was, however, based on a misconception. Cope in 1897 and Hay (317) referred the species to _Sauropleura_, where it is retained. The species is represented by a single individual preserved on a block of coal from Linton, and is also indicated by an interclavicle and its obverse; this element is of larger size than that of the type and was referred by Cope to _Colosteus pauciradiatus_. The characters of the plate are, however, so identical with those of the interclavicle in the type specimen that it is unhesitatingly referred to the present form. The type specimen consists of the supero-lateral view of a crushed cranium with the anterior part of the body, exhibiting the interclavicle and the ventral scutellation. No limbs have been observed in this species. The mandibles are crushed across the cranium in such a way as to obscure its structure. The boundary of the left orbit is doubtfully determined as being a little back of the median line of the skull. There are small teeth present on the mandibles, but their number can not be determined. The cranial elements are sculptured with radiating grooves and ridges, but these are weakly developed. The snout is broad and but little narrower than the base of the skull. (Plate 21, fig. 5.) The interclavicle, somewhat displaced, is the only element of the pectoral girdle preserved. It is peculiar in the possession of a backward extension which shows a beveled edge. The plate is ornamented by radiating grooves and ridges which are strongly developed. The larger specimen of an interclavicle shows the same characters as the one described, and it differs only in being about twice as large. There are no traces of limbs. The ventral armature of the body is rather weak as compared to that of _Sauropleura pauciradiatus_, but it is still composed of closely packed scutes arranged _en chevron_. The character of the ventral armature and the sculpturing of the interclavicle are taken as the principal specific characters. From the other species of the genus the present form differs in its more slender elements of the ventral armor and in the form of the skull. The ribs are not clearly defined. Measurements. mm. Median length of skull 70 Posterior width of skull 40 Anterior width of skull 20 Length of jaw 50 Anterior width of jaw 7 Posterior width of jaw 12 Length of mandibular tooth 1.5 Length of entire specimen 150 Width across belly, maximum 47 Length of interclavicle 27 Width of interclavicle 13 Width across posterior extension 4 =Sauropleura digitata Cope.= Cope, Proc. Phila. Acad. Nat. Sci., p. 216, 1868.