NO. 2177. FOSSIL FISHES IN NATIONAL MUSEUM— EASTMAN. 259 



in allusion to which the specific title was bestowed are the result 

 partly of wear and partly of discoloration along concentric lines of 

 growth, as shown by the arrangement of the pores in which the fine 

 tubules terminate. 



A number of well preserved examples of tliis species, all from the 

 St. Louis Hmestone, are contained in the National Museum collec- 

 tion. An imusually large-sized grinding tooth, collected by G. Ham- 

 bach, is shown of shghtly less than the natural size in plate 7, fig. 8. 



Formation and locality. — St. Louis limestone; near St. Louis, 

 Missouri; also Ilhnois and Michigan. 



Family COCHLIODONTIDAE Owen. 

 Genus PSEPHODUS Agassiz. 



As in Cocliliodus, so also in Psephodus and closely alUed genera, it 

 is probable that a series of helodoid teeth was associated in the same 

 mouth as the large posteriorly placed grinding plates, which latter 

 have resulted from the fusion of a double series on either side of the 

 jaw above and below of narrow and elongate elements. A review of 

 the Uterature describmg the association of Pscpliodus and Ilelodus- 

 Hke teeth has been given by E. B. Branson; ^ and the conclusion 

 reached by this author is that probably m Cocliliodus as well as in 

 Psephodus no helodoid teeth were present in the complete dentition. 

 Branson's view, wliich is directly contrary to the prevailing opmion 

 of palaeichthyologists, is based upon his interpretation of the type of 

 the following-named species. 



PSEPHODUS LEGRANDENSIS Branson. 



Plate 18, fig. 2. 

 Psephodus legrandensis Branson, Joum. Geol., vol. 13, 1905, p. 24, pi. 1, fig. 2. 



The unique specimen serving as the type of this species shows the 

 two series of crushing plates belonging to both halves of the same 

 jaw, and it is supposed by the original author that these elements lie 

 in their imdisturbed natural position. It is further supposed by him 

 that they were preceded in front by a pair of small-sized triangular 

 teeth wliich were in contact with each other along the median 

 line. According to this conjectural reconstruction, as stated by the 

 author,^ "no place remains on the jaw for the helodoid teeth which 

 have been so generally considered as forming a component part of 

 the dentition of this genus. 



Through the kindness of Dr. Stuart Weller, of the University of 

 Chicago, the present writer has had the privilege of examing the type 



1 Branson, E. B., Notes on some Carboniferous CocMiodonts, with descriptions of seven new species. 

 Joum. Geol., vol. 13, 1905, pp. 20-34. 

 'Idem, p. 20. 



