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Show 602 . i ON THE SKULL OF THE LEPIDOSIREN. [June 1, that in the winter of 1891, during an afternoon walk just outside the walls of Cairo, on the desert side of the town, I came across a large Weasel with a yellow throat, which on m y approach ran off and took refuge in a hole in the old city walls." Frofessor T. W. Bridge, E.Z.S., read a memoir on " The Morphology of the Skull in the Earaguayan Lepidosiren and other Dipuoi." The first portion of this paper treated in detail of the structure of the skull in one of the specimens of Lepidosiren collected in the region of the Baraguay river by the German traveller Dr. Bohls. In the second portion was included a revision of the cranial structure of Ceratodus and Protopterus, and a detailed comparison of the two genera with one another and with Lepidosiren. As compared with Protopterus, the most noteworthy distinctive features of the skull of Lepidosiren were stated to be :- (a) The further atrophy of the occipito-periotic portion of the chondrocranium, and the reduction in height and thickness of the tubercular rods which form the connection between the occipito-periotic and ethmo-nasal regions. (o) The extension of the antorbital cartilages into the upper labial folds as far forwards as the extremity of the snout. (c) The rotation backwards of the axis of the suspensorial cartilage to a greater extent than in either Protopterus or Ceratodus: hence it followed that the suspensorium made a more open angle with the fore part of the basicranial axis than was the case with either of the two last-mentioned genera. (d) The greater development of the fronto-parietal bone, which not only completely covered the dorsal surface of the cranium, but also invested the auditory capsules, formed the lateral bony cranial walls of tbe interorbital region, and, moreover, strengthened each suspensorial cartilage by investing its outer surface nearly as far ventrally as the articular condyle for the lower jaw. In comparing the three types the conclusion arrived at was, that the skull of Ceratodus was by far the most generalized and primitive, and further, of the two remaining genera the skull of Lepidosiren represented but a slightly more specialized type than that of Protopterus. Briefly, it might be affirmed that if the skull of Ceratodus were taken to represent a relatively early larval stage, those of Protopterus and Lepidosiren were comparable to two immediately succeeding but much later stages, while, with one or two exceptions, the differences between the two latter genera were much the same in nature and extent as those which, for example, characterized the skulls of first and second year frogs. The third section of the paper included a brief summary of the present state of our knowledge of the structure of the skull in the fossil Dipnoi, and a comparison of it with existing types. On the evidence afforded by the skull alone, it was inferred that Ceratodus was the most primitive of known Dipnoi, and that Protopterus and Lepidosiren were the specialized and direct descendants of some Ceratodus-\ike ancestor. Of the fossil Dipnoi, Clenodus certainly, |
