OCR Text |
Show 660 MR. A. SMITH WOODWARD ON THE SO-CALLED [Nov. 20, teeth, laterally compressed but without trenchant edges. There is also a pair of still larger teeth of a similar character immediately within the symphysis of the mandible. All the teeth are smooth. The preoperculum (fig. 1, p.op.) is relatively thin, broad at its angle, and marked with radiating sensory canals. The limits of the operculum and suboperculum are not quite clear; and of the branchiostegal rays it can only be said that they are numerous, perhaps about 20 on each side. A gular plate may or may not have been present, but no remains of it are preserved. The centra of the anterior abdominal vertebrae are deeper than long, and strengthened by peripheral secondary calcifications in the form of irregular longitudinal ridges. The scales are large and smooth. As shown by the characters of its dentition, the fossil thus described evidently pertains to a genus distinct from that to which Osmeroides lewesiensis is referred. In the absence of the trunk, however, it is difficult to determine its precise position ; and it can only be said to approach most nearly the Ehps-h\e fishes from the Chalk of Bohemia and Dalmatia to which the generic name Elopopsis has been applied. It agrees with these especially in the nature of the dentition, the form of the mandible, and the characters of the preoperculum. As a temporary expedient, the Brighton fossil may therefore bear the name of Elopopsis crassus. 3. AULOLEPIS TYPUS. (Plate XLIII. figs. 2-6.) Auhlepis typus, L. Agassiz, Poiss. Foss. vol. v. pt. i. p. 14, pt. ii. p. 109, pi. lx.a. figs. 5-8 (1834-44) ; A. S. Woodward, Proc. Geol. Assoc, vol. x. p. 324 (1888). Another generic type from the English Chalk commonly regarded as a Salmonoid is named Aulolepis. Only a single species, A. typus, is known ; but this is represented by so large a series of specimens in the British Museum that it makes an important contribution to our knoAAdedge of the osteology of the Cretaceous physosto-matous fishes. The head is known almost exclusively by the external bones. The cranial roof (fig. 2) is flattened mesially, but someAA'hat arched downwards at the lateral margin; and the occipital border is either straight or Avith a slightly re-entering angle. The supra-occipital exhibits a median vertical keel on its hinder face, but the bone is almost or quite excluded from the superior aspect of the skull. The parietals (p>a.) meet in an irregular Avavy suture, as also does the hinder portion of the frontals (fr.), and the former bones scarcely attain one-third of the length "of the latter; the transverse suture between these two pairs of elements is likewise unsymmetri-cally wavy. The squamosals (sq.) are as broad as the parietals, but extend further forwards on the outer margin in a narrow process. Each frontal (fig. 3) is very broad behind and much tapering in front, while the longitudinal sensory canal opens on its surface in a series of small pores. The ethmoidal region of the cranium can only be described as narrow, not much expanded at the extremity. |