1914] 



Bryant: Teeth of a Cestraciont Shark 



29 



so highly arched, and the dome-like prominence is not nearly so 

 marked. Reticulations radiate from a point on the crown corre- 

 sponding to that, in the teeth previously described. A small fragment 

 of a tooth (no. 20046), is probably of the same type. 



The greater number of the fossil cestraciont fishes are known only 

 by dorsal fin-spines or by teeth. The fact that these more resistant 

 parts are seldom fonnd associated has doubtless led to a duplication of 

 names. Woodward's 1 method of grouping the species described from 

 fin-spines in one genus, and those described from teeth in another until 

 further evidence is obtainable, is worthy of imitation. The cestraciont 

 teeth at hand, resembling those of the European genus Aster acanthus 

 Agassiz, 2 are placed in the provisional genus Strophodus Agassiz, 

 "species founded on detached teeth not yet correlated with dorsal 

 fin-spines." 



In Europe and America there are a number of genera of cestra- 

 ciont fishes based on fin-spines and on teeth similar to those at hand. 

 The genera Aster acanthus, CtenacantJius, Orecanthus, Nemacanthus, 

 Glymmatacanthus, Bythiacanthus, and Cosmacanthus are the best 

 known. 3 



The type specimen of Aster acanthus ornatissimus Agassiz (Stro- 

 phodus reticulatus) comprises both a spine and teeth. The teeth of 

 Strophodus shastensis differ from those of A. ornatissimus in the ab- 

 sence of a longitudinal keel on all of the teeth. The teeth of S. 

 shastensis are in addition much narrower, and not so distinctly quad- 

 rate as those of A. ornatissimus. 



Fin-spines have been recorded from the Subcarboniferous of 

 Illinois, Tennessee, and Missouri, and one from the Lower Triassic of 

 Idaho. The latter was placed in the genus Cosmacanthus by Evans. 4 

 One originally described from the Lower Carboniferous of Tennessee 

 by Leidy 5 was referred to the genus Aster acanthus. St. John and 

 Worthen" later referred this specimen to the genus Bythiacanthus 



1 Woodward, A. S., Catalogue of the fossil fishes in the British Museum 

 (London, 1889), vol. 1, 1-474, 17 pis., 13 figs, in text. 



2 Agassiz, L., Recherehes sur les poissons fossiles (Petitpierre, Neuchatel, 

 Suisse, 1838), vol. 3, 1-389. Strophodus, p. 116. 



sZittel, K. A., Traite de Paleontologie (Octave Doin, Paris, 1893), vol. 3, 

 1-894, 719 figs, in text. 



* Evans, H. M., A new cestraciont spine from the Lower Triassic of Idaho, 

 Univ. Calif. Publ. Bull. Dept. Geol., vol. 3, 397-402, 1 pi., 1904. 



5 Leidy, J., Contributions to the extinct fauna of the western territories, 

 Rep. U. S. Geol. Surv. of Terr., F. V. Hayden, U. S. Geologist in charge, vol. 1, 

 14-358, 37 pis., 1873. 



" St. John, O., and Worthen, A. IL, Geological survey of Illinois, vol. 6, viii, 

 1-532, 33 pis., 1875. 



