DEVONIAN FISHES OF IOWA 147 



2. VERTEBRAL CENTRA. 



It is a well known fact that the usual condition of the vertebral 

 axis in Palaeozoic fishes was notochordal, and even in the most 

 advanced forms ossification seldom progressed so far that the 

 vertebral bodies were more than hollow rings. The earliest 

 Elasmobranch bodies of this nature known to Agassiz were of 

 Jurassic age, and the total absence of ossified centra in Palae- 

 ozoic ganoids, even in the most exquisitely preserved Palaeon- 

 iscid skeletons, impressed this ichthyologist as a very singular 

 fact. Inclined at first to attribute their absence to defective 

 preservation, or to post-mortem destructive agencies, such as 

 chemical solution, he afterwards adopted the opinion that is now 

 generally entertained, namely, that in the aggregate of Palae- 

 ozoic fishes the axis never passed beyond the cartilaginous stage. 

 Even in Devonian Lung-fishes, such as Dipterus, Scaumenacia, 

 etc., there were no ossified centra, and the perforated bodies from 

 the Devonian of Novgorod, Russia, that were tentatively re- 

 garded as of Dipterine nature by Pander * have been excluded 

 from such association by Traquair after an examination of a 

 large quantity of Scottish material. f 



Under these circumstances it is interesting to record the fact 

 that a single well preserved vertebral centrum has been brought 

 to light during the spring of last year from the Upper Devonian 

 near Solon, in rocks of the same age as the State Quarry beds 

 north of Iowa City. Mr. J. H. Hoats, one of Professor Calvin's 

 students in geology at the State University, was fortunate 

 enough to discover the specimen while collecting in Johnson 

 county, and the thanks of the writer are due to both master and 

 pupil for the privilege of describing it. An illustration of it 

 is given of the natural size in Plate XII, Fig. 16. 



This unique example of a detached vertebral body is chiefly 

 interesting on account of its geological antiquity. There are 

 no similar contemporaneous structures with which it may be 

 compared, and in the absence of other naturally associated 

 parts, its systematic position can only be conjectured. Ptycto- 



* Pander, C. H., Ueber die Ctenodipterinen des devonischen Systems. St. Peters- 

 burg, 1858. 



t Traquair, R. H., On the genera Dipterus, Palsedaphus, etc. Ann. Mag. Nat. 

 Hist. 1878, ser. 5, 2, p. 10. 



