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Show 1887-] ON THE LATERAL LINK OF SQUALORAJA. 481 information as to the perishable tissues originally associated with the skeletal fragments he finds in the rocks ; and such is all the more to be regretted in the present instance, since the Pteraspidian fishes are the earliest undoubted members of the class that have hitherto been recognized in geological history. 3. Note on the " Lateral Line " of Squaloraja. By A. SMITH WOODWARD, F.Z.S. [Received April 28, 1887.] In my description of the fossil Liassic Selachian Squaloraja, read before this Society in October last (see P. Z. S, 1886, p. 527), some series of very minute dermal ringlets are noted in the cephalic and caudal regions, and these are regarded as designed for the strengthening of the edges of those flattened parts of the body. They are marked by the letter cl adjoining the rostral cartilages in fig. 1, pl. Iv. loc. cit., and are also shown in connected series along the tail, parallel to an irregular dermal ridge which is similarly designated. They are, moreover, seen in the original of fig. 3, and in the caudal region of the specimen previously figured by Davies. Subsequent studies have led me to determine that these curious structures are truly the supports of the canal of the "lateral line." In the living Chimcera, the open groove in which the sense-organs are lodged is strengthened throughout by precisely similar rings, as originally observed by Stannius" and Leydig 2, and figured and described by the latter; and von Meyer3 has likewise discovered these calcifications in a closely-allied fossil form from the Upper Jurassic of Bavaria. They have been aptly compared with the tracheal rings of some small air-breathing vertebrate. Their remains upon the tail show that they were incomplete, exactly as in the existing genus just mentioned; and we may therefore conclude that Squaloraja was characterized by an open sensory canal of the essential Chimseroid type. The circumstance adds one more to the series of points in which the old Selachian seems to be related to the last-named order, and it is thus particularly worthy of note. 1 H. Stannius, Lehrb. vergl. Anat Wirbelthiere, 1846, p. 49. 2 F. Leydig, " Zur Anatomie und Histologie der Chimcera monstrosa, Muller s Archiv, 1851, p. 251, pl. x. fig. 2. 3 H. von Meyer, " Chimcera (Ganodus) avita, aus dein lithographischen Schiefer von Eichstatt," Pabeontographica, vol. x. (1862), p. 92, pl. xii. |