ART. XXXV. - ON THE GENUS ERISICHTHE.

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By E. D. COPE.

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     Erisichthe is a genus of fishes which was described by the writer in 1873, and subsequently referred to the Saurodontidæ. In the Final Report of the United States Geological Survey of the Territories*, the typical species, E. nitida, was again described, and also figured, so far as the material permitted, and the existence of a second species, E. angulata, § was pointed out. Subsequent accumulation of material enables me to add to the knowledge of the structure of the genus and to increase the number of known species.

     The E. nitida Cope was originally represented by a few portions of the skull; among other pieces, the premaxillary and dentary bones being present. The latter element was correctly determined, but the premaxillary was called maxillary in my description. A fine specimen of the species, obtained the present season from the Niobrara Cretaceous of Kansas, by Charles H. Sternberg, includes the greater part of the cranium. From this and other specimens I discover that the anterior portion of the skull, probably the ethmoid bone, is produced into a long beak, in general form similar to the sword-like snout of the Sword-fishes of modern seas. I had already been in receipt of fragments of these beaks, associated with loose teeth of the genus Erisichthe, but it was Prof. B. F. Mudge who first pointed out that both belong to one and the same genus.§§ The specimen above mentioned includes also the maxillary bones, so that their true character is now clear. A remarkable feature of the genus is displayed in the mandibles. Each of these is compound in the region usually composed of the simple dentary bone. It there consists of three parallel elements, an internal and an external embracing a median element. The inner bears a band of teeth en brosse on its inner and superior aspect, and the external a few teeth of similar character on its superior edge. The large lancet shaped teeth are borne by the middle element, excepting some of the largest near the symphysis. Two of these on the inner side of the ramus originate in the internal bone. The maxillary bone forms the greater part of the arcade of the mouth, and has no superior articulation with the facial part of the skull. It is attached by a simple sutural articulation with the premaxillary, so as to permit some lateral motion. The premaxillary also ________________________________________________________

         * Vol. ii, 1875, p. 217, pl. xlviii, figs. 3-8.

             § Portheus angulatus, Geolog. Survey N. Carolina, by W. C. Kerr, p. 32.

             §§ Bulletin U. S. Geol. Survey Terrs.

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822         BULLETIN UNITED STATES GEOLOGICAL SURVEY.

has no superior condyle articulating with the cranium, but the entire length of its superior margin is applied in a groove of the ethmoid bone, so as to be immovable. Anterior to the premaxillary bones, on the inferior aspect of the ?ethmoid, is situated a pair of large, compressed, double-edged teeth, whose alveoli are close together. Only one of these teeth is in functional service at a time. In the Erisichthe penetrans, the superior surface of the skull is swollen above the fundus of this alveolus, while no such enlargement marks the position of its young companion.

     The compound character of the mandible, and the peculiar mode of articulation of the premaxillary and maxillary bones, entitle this genus to recognition as the type of a family distinct from the Saurodontidæ, which may accordingly be called the Erisichtheidæ. It is allied to the Saurodontidæ in the mode of implantation of its teeth and in the relative extent of the bones of the maxillary arch.

     Three species are represented by the specimens received. They are readily distinguished by the forms of the beak. In the E. nitida, this weapon is distinguished by the flat superior surface of its distal half. The section in this region is semicircular, a strong angle on each side bounding the superior plane, while at the base the section is a transverse oval. The flat surface is only finely rugose, while the remainder is closely marked with raised ridges, which are general parallel, but which send off many lateral free or inosculating branchlets. This beak is stout, and contracts abruptly at the tip. It is also recurved, and the form does not appear to be due to distortion. Length from the inferior pair of large basal teeth 0^m.155; transverse diameter at base 0^m.025; depth at base 0^m.021.

     The second species, which I call Erisichthe penetrans has a snout of uniformly oval section at all points. The long diameter of the section is transverse. The axis is straight and the form acuminate, the contraction .being uniform and gradual to acute apex. Thus it follows that a beak of greater diameter at the base than one of the E. nitida has a more slender shaft. The teeth of the inferior basal pair are, in the specimen described, of large size, and, as in other species, smooth, compressed, and with opposite fore and aft cutting edges. The surface of the beak is thrown into numerous sharply defined longitudinal ridges, which are more or less inosculate with each. There is no difference between the superior and inferior surfaces in this respect. Length of beak from basal teeth 0^m.150 ; transverse diameter at base 0^m.035 ; vertical diameter at the same point 0^m.020 ; width at middle of the fossæ for the premaxillary bone 0^m.060.

     The third species of Erisichthe is represented by a muzzle of an old individual, which has lost a good deal of its apex by attrition. Its surface lacks the sculpture of the other species; but whether this smoothness is due to attrition or not is uncertain. The alveolæ for the basilar teeth are empty and almost filled up with bone. The form of the muzzle is quite

                       COPE ON THE GENUS ERISICHTHE.                         823

peculiar. Its shaft is depressed, with a strongly convex inferior surface and a slightly convex superior surface, the two separated by an obtuse angular border. Behind the alveolæ, the inferior surface is narrowed by a strong lateral contraction, in which the superior surface shares in a slight degree. The latter is continued in a prominent border. The inferior surface is divided by an angular depression, the apex of which is directed forward. It is perhaps the articular face for the extremity of the vomer. As compared with the other species, this one is characterized by the lateral longitudinal concavity at the base, which appears to be an anterior prolongation of the grooves for the premaxillary bones. The small size and anterior position of the alveolæ of the basal pair of teeth is also a marked character. The superior surface of the skull at the base of the beak is apparently unworn; it is smooth. In E. nitida, it is sculptured with ridges. Length preserved, anterior to dental alveolæ, 0^m.045; transverse diameter in front of alveoli 0^m.025; vertical diameter 0^m.020. This species may be called E. ziphioides, from the Ziphias-like form of the beak.

     A fourth species has been found in England, and figured by Dixon in the "Geology of Sussex". The portions represented in this work are the mandibles, which resemble those of the E. nitida, an which were supposed at that time to belong to a species of Saurocephalus. A muzzle, perhaps of the same species, was regarded as a Sword-fish, which was called Xiphias dixonii by Agassiz. It should be now termed Erisichthe dixoni.