148 . IOWA GEOLOGICAL SURVEY 



dont remains being represented in far greater abundance in 

 the same formation than any other group of fishes, and tritors 

 of P. calceolus surpassing all the rest in point of numbers, there 

 is a strong temptation to make this theoretical association of 

 parts. 



The specimen is here considered under the head of detached 

 parts accompanying Ptyctodont remains because this is a con- 

 venient place to speak of it, and also because it does not seem to 

 us a too remote contingency that the body actually belongs to 

 Ptyctodus or one of its congeners. At the same time it must 

 be acknowledged as a very remarkable fact that similar bodies 

 have not been brought to light elsewhere in association with 

 Ptyctodont remains, especially in localities where these remains 

 are well preserved, as at Waterloo, or Milwaukee, or the Upper 

 Devonian of Wildungen, Germany. And above all we must not 

 be forgetful that this elongate centrum is strikingly dissimilar 

 to the narrow "rings" observed in those Chimaeroids where 

 the axis is segmented, and that in the existing Callorhynchus 

 no trace of axial segmentation is to be seen at all. Hence the 

 occurrence of calcified vertebral bodies in Ptyctodonts, of the 

 form presented by Mr. Hoats' specimen, would be a character 

 difficult to reconcile with their supposed Chimaeroid affinities. 

 The centrum looks as if it belonged to fishes of a higher grade 

 than Chimaeroids, or even Dipnoans, but as we know of abso- 

 lutely no other remains with which they might be theoretically 

 associated, the conjecture is allowed to stand that it may be of 

 Ptyctodont nature. 



The original specimen obtained by Mr. Hoats is now deposited 

 in the Museum of Comparative Zoology. It is of moderate or 

 rather small size, measuring 1 cm in length, and approximately 

 1.2 cm in diameter, allowing for a slight deformation due to 

 mechanical pressure prior to or during fossilization. The inter- 

 vertebral faces are deeply biconcave, and apparently perforated 

 by a small central opening for passage of the notochord. In the 

 present condition of the specimen, however, it cannot be posi- 

 tively determined whether the orifices seen on either face are 

 continuous throughout the substance of the vertebral body. Some 

 of the problematical Russian specimens are completely perfo- 



