. Chimæroid fishes and their development. Fishes; Chimaeridae. JURASSIC ;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 alread}' 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 co
. Chimæroid fishes and their development. Fishes; Chimaeridae. JURASSIC ;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 alread}' 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 Chimairoid. 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- 133 m 'S^S&^^S^ 135. ing organs. The frontal clasper is still a Figs. 132-137.—Evolution of frontal clasping spine ot Chim- aeroids, 132. Fir-spine o( Myriacanlhus. 133. Frontal clasping spine o( Squalo- raja. !34. Frontal clasping spine of Myriacanthus. 134 A. Base of clasping spine of Myriacanthus, ventral aspect, to show areas of attachment of muscles. 135. Frontal clasping spine of Ischyodus. after specimen in Munich M
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectfishes, bookyear1906
