. Carnegie Institution of Washington publication. JURASSIC CHIM.^ROIDS. 141 and extended in their lines of attach- ment forward as far as the antero-lateral clasping organ.* This is of particular interest, since it in- dicates, as we have already noted, that the antero-lateral clasping organ was probably, as Gegenbaur, Garman, and Agassiz suggested, a modified radial car- tilage (possibly a number of radial car- tilages), but up to the present time there has been no evidence which has bridged the wide gap between the antero- ventral clasper and the true radial cartilages. The condition of the
. Carnegie Institution of Washington publication. JURASSIC CHIM.^ROIDS. 141 and extended in their lines of attach- ment forward as far as the antero-lateral clasping organ.* This is of particular interest, since it in- dicates, as we have already noted, that the antero-lateral clasping organ was probably, as Gegenbaur, Garman, and Agassiz suggested, a modified radial car- tilage (possibly a number of radial car- tilages), but up to the present time there has been no evidence which has bridged the wide gap between the antero- ventral clasper and the true radial cartilages. The condition of the mixip- terygium is also significant, for it is here short and wide, its base in one specimen suggesting clearly its origin in a cluster of radial cartilages. One observes, also, that the shagreen which encases this organ is not limited to its tip, but extends proximally almost to its base, a condition which has been retained so completely in no living Chimseroid. It may be noted, finally, that a mucous-canal sys- tem is present whose supports are arranged in rouleaux of minute rings, a condition which exists in a somewhat rudimentary form in recent genera. Summarizing, then, our knowledge of Squaloraja, we find that this early Chimseroid was shark-like in the follow- ing regards: (i) In dermal defenses, exhibiting as it does an investiture of shagreen. (2) In the width of the mouth, which shows definitely that it had not yet attained the beak-like character of the mouth of recent forms. (3) In the undifferentiated condition of the clasp- ing organs. The frontal clasper is still a J33 m 135. Fig$. 132-137.—^Evolution of frontal clasping spine of Chim- aeroids. 132. Fin-spine of Myriacanthus. 133. Frontal clasping spine of Squalo- raja. 1 34, Frontal clasping spine of Myriacanthus. I 34 A. Base of clasping spine of Myriacanthus. ventral aspect, to show areai of allachment of muscles. 135, Frontal clasping spine of Ischyodus. after specimen in Munich Museum. 136. Frontal claspin
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