Fishes . nings on the side,and the rays in another (Rajar, Batoidci, Hypotrema) havingthe gill-openings underneath. Of far more importance thanthis superficial character of adaptation are the distinctionsdrawn from the skeleton. Dr. Gill has used the attachmentof the palato-quadrate apparatus as the basis of a Opistharthri {Hexanclud<z) have this structure articulatedwith the postorbital part of the skull. In the Prosarthri {Hetero-donUda) it is articulated with the preorbital part of the skull,while in the other sharks (Anarihri) it is not articulated at these ch
Fishes . nings on the side,and the rays in another (Rajar, Batoidci, Hypotrema) havingthe gill-openings underneath. Of far more importance thanthis superficial character of adaptation are the distinctionsdrawn from the skeleton. Dr. Gill has used the attachmentof the palato-quadrate apparatus as the basis of a Opistharthri {Hexanclud<z) have this structure articulatedwith the postorbital part of the skull. In the Prosarthri {Hetero-donUda) it is articulated with the preorbital part of the skull,while in the other sharks (Anarihri) it is not articulated at these characters do not appear to be always , for example, differs in this regard fromHeptrancliias, which in other respects it closely resembles. Yet,in general, the groups thus characterized are undoubtedlynatural ones. The sharks are among the earliest fishes to appear in therocks, and from primitive sharks all the higher groups offishes are descended. The earliest known and lowest in. Fig. 125.—Clndosclache fyleri (Newberry), restored. Middle Devonian of Ohio. (After Dcau.) structure constitute the order Pleitropterygii [Cladoselachidcc),typified by Cladoselache jyleri from the middle Devonian ofOhio. I 84 The True Sharks Order Notidani.—We may recognize as a distinct order aprimitive group of recent sharks, a group of forms finding itsnatural place somewhere between the Cladoselachidcc and Hctcro-dontidcc, both of which groups long preceded it in geologicaltime. It has been lately announced that a ruaimentary sixth gill-arch exists in Heterodonliis. This would show the close afilnityof these two primitive groups, Notidani and Cestractontes, andthe latter should be removed from the Asterospondyli. Thepresence of five species in the Squalidcc perhaps indicates affinitywith Heterodontus. The fact that Cestraciontes wtre the onlysharks living in the Triassic, soon followed by Xotidani and laterby squaloid and galeoid sharks, seems to be significant. The n
Size: 3303px × 757px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisher, booksubjectfishes
