264 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



tain details; together they acquaint us with the entire outline, includ- 

 ing the part mserted m the integument, and also show the characters 

 of the superficial ornamentation more clearly than in the original 

 illustrations of this species. 



At first sight it may seem peculiar that the large, obliquely directed 

 denticles seen along the concave margin near the distal extremity 

 should occur on the anterior, instead of posterior, face of the spine. 

 Similar conditions, however, have been noted by St. John andWorthen 

 in the form described by them as Xystracantlms [ = Physonemus] 

 mirdbilis, and the like is to be observed also in the still more arcuate 

 and forwardly curved spmes from the Russian Coal Measures which 

 have been theoretically associated by Inostranzev^ and JaekeP with 

 the teeth of Polyrhizodus rossicus. We should not hesitate to refer 

 these Russian spmes to the genus Physonemus, and the interpretation 

 that we should place upon them is to regard them as frontal clasping 

 organs, of the same nature as those in Squaloraja, Myriacanthus, and 

 recent Chimaeroids. 



A single arcuate spine, much weathered and preserved partly in 

 the form of an impression, but apparently referable to this species, 

 was obtained by J. A. Udden in 1914 from Pennsylvanian strata near 

 San Sabo, Texas, at the same locahty that yielded the type of Dic- 

 renodus texanus. It is contained in the Museum collection (Cat. 

 No. 8108) and is shown in plate 5, figure 3. 



PHYSONEMUS ARCUATUS M'Coy. 



Plate 5, figs. 1, 2. 



Physonemus arcuatus M'Coy, Ann. Mag. Nat. Hist., [2] vol. 2, 1848, p. 117, and 

 Brit. Palacoz. Foss., 1855, p. 638, pi. 3 I, fig. 20.— Eastman, Bull. Mus. 

 Comp. Zool., vol. 39, 1903, p. 208, text-fig. 12. 



Spines of this species are of extremely rare occurrence in the Lower 

 Carboniferous of the Mississippi Valley, and few perfect examples 

 have been obtamed from either this country or Great Britain. In 

 general the known specimens are denuded of their superficial orna- 

 mentation, and the denticles along the concave margin are either 

 worn or broken away. Two specimens which show the tuberculate 

 ornamentation more perfectly than m any previously described 

 example of this species are preserved in the Museum coUection, and 

 illustrated in plate 5, figures 1 and 2. They differ somewhat m gen- 

 eral outline, one bemg slender and erect, and having the posterior 

 denticles more strongly developed than in the other, wtiich is more 

 compact and arcuate. Nevertheless, we are not mclined to regard 

 these differences as sufficient to warrant the establishment of a new 



» Travaux Soc. Nat. St. P^tersb., vol. 19, ISSS, pp. 1-18, with plate. 



2 Zeitschr. Deutsch. Geol. Ges., vol. 51, 1899, p. 281, text-fig. 5. The ornamentation of these spines is 

 suggestive of certain species of Oracanthus. 



