New Genus of Fishes from the Niobrara

Cretaceous.

Contribution from the Paleontological Laboratory, No. 46.

BY S. W. Williston.

With Plate XXVI.

Leptecodon rectus, gen. et. sp. nov.

     Slender and elongate; head elongate, the jaws slender, the anterior extremity in the specimen wanting. The hind end of the mandibles is represented by an impression situated below the posterior end of the skull. Teeth numerous, small, pointed, slender. The orbit is situated posteriorly, is of moderate size and round. Scapular arch strong, the large opercular space in front showing   indications of the thin opercular bones. Vertebræ about forty-five in number, elongate, more than three times as long as deep, much constricted in the midline. Pectoral fins small, composed of seven or eight rays. Ventral fin very small, situated about the middle of the vertebral column; caudal fin small, the rays feeble, evidently cartilaginous, the outline indicated on the stone: the shape of the fin is regular apparently, the angles produced. Other fins wanting or not preserved. The side of the body as preserved, shows three longitudinal rows of large, firmly united scutes, apparently of the same number in each series as the vertebræ. The scutes are in the form of a double trapezium, with the V posterior, the middle raised into a well-marked carina, which runs from the head to the tail. Apparently there are five rows of these scutes on the body. At the front the topmost row is near the middle line, the lateral row has its lower edge over the line of the vertebræ, while the lowest row has the carina just below the pectoral fin. The scutes have a finely roughened appearance, due to minute, rounded and shallow pits There are no indications of small scutes on the body intermediate between the larger ones.

            (113) KAN. UNIV. QUAR. VOL. VIII, NO. 3, JULY, 1899, SERIES A.

114 KANSAS UNIVERSITY QUARTERLY.

Length of fish, as preserved …………………………….240 mm

Estimated length ………………………………..………..250 "

Length of vertebral column ……………………..……….175 "

Greatest width, just back of pectoral fin. ……….……….. 27 "

Length of caudal fin, upper lobe. …………………..…….. 22 "

Length of pectoral fin ………………………………....…… 7 "

Length of ventral fin. …………………………………...….. 9 "

     The specimen lies on the shell of a large Inoceramus, explaining its excellent preservation. Close by are the remains, as seen in the illustration, of several examples of a small fish of unknown affinities, hitherto undescribed. The horizon is the Niobrara Cretaceous of the Smoky Hill River. The specimen was collected by Mr. H. T. Martin in 1895.

     The family Hoplopleuridæ, in which this genus must for the present be placed, includes apparently heterogeneous forms, and concerning which there is a diversity of opinion. The definition of the family, as given by Zittel, will not include the present genus, and perhaps some others located in it by that author. He includes the following genera: Belonorhynchus, Saurichthys, Saurorhamphus, Euryophilus, Palimphemus, Pantophilus, Eurygnathus, Plinthophorus, Dercetis, Leptotrachelus, ?Aspidopleurus and Pelargorhynchus, all from the Cretaceous. Blochius is placed by him in a separate family, the Blochiidæ.

     Belonorhynchus and Saurichthys are located by Woodward in another family, the Belonorhynchidæ, widely separated from the Hoplopleuridæ. Lydekker, in his Manual, includes in this family the following genera: Dercetis (Leptotrachelus), Aspidopleurus, Blochius, Plinthophorus, Pelargorhynchus and Saurorhamphus. Euryophilus he locates in the allied family Enchodontidæ.

     The family Hoplopleuridæ was established by Pictet for fishes which were devoid of scales properly so-called, but which are protected on the back and sides by rows of scutes. The head is long and the jaws are provided with pointed teeth of unequal size. The bones of the head are frequently sculptured or granulose. The genera associated in this family by M. Pictet are: Dercetis Agassiz, Saurorhampus Heckel; Leptotrachelus v. d. Marck; Plinthophorus Günther; Euryophilus Pictet; Pelagorynchus v. d. Marck. The fishes included in the genus Dercetis were considered by Agassiz to resemble the sturgeons in the arrangement of the dermal scutes, and were grouped amongst the Ganoids. Heckel held the same opinion with respect to the position of Saurorhamphus, and Von der Marck also places the genera Pelargorhynchus and Leptotrachelus

                                 WILLISTON: A NEW GENUS OF FISHES.                          115

amongst the Ganoids, but regards Ischyrocephalus as a Teleostean. A careful review of the whole of the genera, assisted by additional specimens of Leptotrachelus and Euryophilus discovered in the chalk of Mount Lebanon, convinced M. Pictet that they formed a group naturally associated, especially by the great analogy afforded by the peculiar arrangement of the series of scutes, and that they formed a family of the Teleosteans, to which he gave the above name.*

     Cope long ago described three species and two genera of this group of fishes from Dakota, which seem to have been overlooked by subsequent writers.** Concerning the relationships, he says: "The relationship of the family of Dercetiform fishes has been discussed by various authors, especially by Pictet and Von der Marck. The former regards them as Teleostei; the latter as "Ganoids." As I do not adopt the division signified by the last name, I find Professor Pictet's view nearer to the point. The specimens indicate further that the Dercetidæ belong to the Actinopteri, and probably to the order Hemibranchii. The only alternative is the order Isospondyli, and the characters which separate the two are not clearly shown in the specimens, Distinct bones below the pectoral fins may be interclavicles, which belong to the Hemibranchii."

     The genus Triænaspis, from the Niobrara of Dakota, there described, has the dorsal and ventral scuta triradiate, the median branch of the three directed anteriorly, together with numerous band-like scuta. Ichthyotringa Cope, from the same locality, has the body covered with small round scales. The third species is Leptotrachelus longipennis Cope, in which the dermal scuta consist of median, dorsal, and ventral rows of tripodal form.

     From all these as well as other forms the present genus seems amply distinct, though evidently nearest allied to Aspidopleurus Pictet and Humbert, from the Lebanon Cretaceous.*** This genus has not been sufficiently well described to be assured of its more important characters, but the present form evidently differs in the shape of the head, fins, scutes, etc.

The present fish has a curious resemblance to the Pipe Fishes.

* Davis, on the Fossil Fish of the Cretaceous Formations of Scandinavia. Trans, Royal Dubl. Soc, iv, p. 428.

** Bull. U S. Geol. Surv., Terr. iv. 67.

*** Pictet and Humbert, Nouv. rech, s. les, Poissons fossiles du Mont Liban, p.l09, pl. x, f. 1; Davis, On the Fossil Fishes of the Chalk of Mount Lebanon, Trans. Royal Soc., iii, pl. xxxviii, f. 4.