242 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



the fact that the type-species of the supposed new genus ^^Dypty- 

 chosteus" is named tesselatus, a title under which another species of 

 Psammosteus had been previously described by Traquair.^ If at some 



future time the Dorpat 

 plate should be proved to 

 be distinct from Psam- 

 mosteus faradoxus, a new 

 specific designation must 

 be apphed to it. For the 

 present, however, we pre- 

 fer to regard the term 

 "DyptycJiosteus tesselatus'^ 

 as a synonym of P. panv- 

 doxus. Also, as far as one 

 may judge from the pub- 

 lished figure of the plate 

 called by the Dorpat 

 author Psammosteus im- 

 perfedus, this would 

 appear to be one of the 

 dorsomedian plates of 

 C eras pis carinata Schliiter. 

 The type material upon 

 which the last-named spe- 

 cies was founded is now 

 preserved in the Museum of Comparative Zoology at Cambridge, 

 Mass. A side view of one of the dorsomedian plates of this form is 

 shown in plate 11, figure 1. 



HOLOCEPHALI. 



Family PTYCTODONTIDAE Smith Woodward. 



The typical genus of this family, Ptyctodus, which is at the same 

 tune the most abundant and widely distributed of any belonging in 

 the same association, was estabhshed by Pander in 1858, upon the 

 evidence of detached "teeth," or tritors as they are more properly 

 called, found in the Middle Devonian of the Governments of St. 

 Petersbm-g, Novgorod, and the Russian Baltic Sea provinces. In the 

 National Museum collection are contained a number of interesting 

 fish-remains from these localities m northwestern Russia, and also 

 from the vicinity of Dorpat. These consist of Ptyctodus tritors (from 

 Babino, Novgorod), Dendrodus, HoloptycMnus, Psammosteus, and 



1 Proc. Roy. Phys. Soc. Edinb., vol. 13, 1897, p. 377, pi. 11, figs. 1, 2. 



Fig. 1.— Dorsomedian shield of Psammosteus paradoxus 



AGASSIZ, wanting SUPERnCLU- ORNAMENTATION. UPPER 



Devonian, Neuhausen, Livonia. (After A. S. Wood- 

 ward AND PrEOBRAJENSKY.) 



