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Show 530 MR. A. S. WOODWARD O N [Dec. 7, of the vertebral column. But the detached spines would appear to afford evidence of two or more forms as yet unrecognized, and the small example, no. VIIL, is particularly distinct. It is very possible, indeed, that when more specimens of the genus are available for study, the characters of the rostral appendage will enter prominently into the diagnosis of each species ; but I only venture, on present evidence, to distinguish the possessor of the small spine no. VIII. (Plate LV. fig. 6), and this may be appropriately designated by the name of S. tenuispina. The fossil in question is separated from its homologue in the known species by its much more slender and acuminate shape, and possibly, though not certainly, by the slight concavity of the proximal half of its upper surface. During the investigation of these fossils I have had the privilege of discussing the subject with several zoological and palseontological friends, to whom I am indebted for some valuable suggestions noted in the following pages. I desire especially to return thanks to Prof. W . K. Parker, F.R.S., for much kind assistance in regard to the skull; to Mr. G. B. Howes, for a continuance of the help so freely given on previous occasions; to Mr. G. A. Boulenger, for the facilities afforded in the study of the recent Selachians under his care ; and to m y senior colleague, Mr. William Davies, to whose earlier work reference is so frequently made in the sequel. ANATOMICAL DESCRIPTION. External Form.-Commencing the description with a brief notice of the general external form of Squaloraja, attention may be first directed to the beautiful specimen no. I., represented in Plate LV. fig. 1. As the shape of the head had already led Agassiz and Davies to suspect, the proportions are found to be very similar to those of the living Pristiophorus. Assuming that about three centimetres are missing from the tail of the specimen, the snout will have occupied one quarter of the entire length of the animal. The body must have been but slightly compressed from above downwards, and the pectoral fins were undoubtedly free, having no connection with the head; the shoulder-girdle, however, is placed relatively nearer to the chondrocraniurn than is the case either in Pristiophorus or Pristis, though appearances are not improbably deceptive, owing to crushing during fossilization. It is impossible, of course, to determine whether the gill-openings were ventral or lateral, and scarcely any traces of the branchial arches have been preserved. The pectoral fins, as usual, are much larger than the ventrals, and the tail is long and slender, without spine, as admirably shown in no. III. (fig. 7). Unfortunately, all sure indications of dorsal and caudal fins are wanting, though it is scarcely likely that these appendages were absent in the living fish. Dermal Structures1.-In regard to the integument and its appendages, the new fossils afford some interesting additional information. No less than eight rostral spines are now available for study ; and ' The dentition will be more conveniently treated in a later section, p. 534. |