CATALOG OF THE FOSSIL FISHES IN THE CARNEGIE MUSEUM. 391 



{Palceos-pinax) are known first from the Lower Lias. These latter have completed 

 vertebral centra, and the Upper Jura furnishes examples of well-formed vertebrae 

 of the types characteristic of modern sharks and rays, that is to say, truly astero- 

 spondylic and tectospondylic vertebral centra. Students of the group are well 

 aware that, as was first demonstrated by Prof. Carl Haase, the time-honored 

 division of Selachii into sharks and rays corresponds very closely to constant 

 differences displayed by the structure of the vertebral bodies. In the rays, or 

 Tedospondyli, a series of concentric lamellae surrounds the primitive double cone 

 of each vertebral centrum; in the majority of sharks (Asterospondyli) the centra, 

 when fully developed, are strengthened by longitudinal ridges or radiating laminae, 

 which, when viewed in transverse section, present a stellate appearance. 



Typical representatives, therefore, of the suborders embracing modern sharks 

 are met with in the fauna of the Lithographic Stone of Bavaria. Nearly complete 

 examples are known of a shark resembling the recent Cestracion (Heterodontus), 

 and the same is true of certain dog-fishes, Scyllium and Pristiurus, while beautifully 

 preserved skeletons of Squatina and Rhinobatus, scarcely to be distinguished from 

 their modern successors, occur in the same horizon. Turning our attention finally 

 to the order or sub-class of Holocephali, this is represented in the fauna under 

 discussion by two genera, Chimceropsis and Ischyodus. The collections of the 

 Carnegie Museum do not contain examples of either of the two last-named genera, 

 but the deficiency is more than compensated by a number of splendidly preserved 

 rays, including a magnificent Rhinobatus from Eichstadt, the counterpart of which 

 is figured in von Zittel's "Handbuch der Palaontologie," Vol. Ill, p. 102. 



An inspection of the subjoined classificatory scheme will permit the major 

 divisions of the class Pisces, which enter into the constitution of the fauna of the 

 Lithographic Stone, to be recognized at a glance. 



Class PISCES. 



Subclass. Order. Suborder. 



(Pleuropterygii) Not represented. 



ilchthyotomi.) " 



(Acanthodei.) " 



Selachii. 



Elasmobranchii 



Plagiostomi 



I Batoidet. 



Holocephali Chimceroidei. 



