656 E. B. BRANSON 



Batacanthus gigas n. sp. (PL IV, Figs. 3-6, and Text-Fig. 4) 



The holotype is a spine with outer and inner ends missing. 

 The part preserved is 26 cm. long, 41 mm. wide at the outer end, 

 and about 65 mm. wide at the inner. If the rate of tapering did 

 not change in the missing parts, about 18 cm. are gone from the 

 outer end and about 8 cm. from the inner. The spine is much 

 compressed, narrowly oval in outline, without flattening on the 

 back edge and with only an indication of an angle on the front. 

 It is so poorly preserved that the ornamentation over most of the 

 surface cannot be made out. Sharp-topped, ribbed denticles lie 

 in close-set rows parallel to the front edge, and the presence of a 

 few elongated, low denticles, set diagonally near the front edge, 

 suggests a type of ornamentation like that in Xystt -acanthus 

 mirabilis St. John and Worthen. 1 



The preservation does not permit of the determination of the 

 angle of insertion of the inner end. The pulp cavity is not large 

 at the inserted end and is open at the back for about 12 cm. After 

 becoming closed it takes its course near the back of the spine. 



This species may be recognized by its large size, oval shape, and 

 ornamentation. 



Spine denticles of an Elasmobranch (PI. II, Fig. 26) 



Isolated specimens of little, cone-shaped denticles shown in 

 this figure are abundant wherever the lowest phosphate bed was 

 examined and several specimens with a number of associated den- 

 ticles are in the collection, but they have not been found attached 

 to spines. In some specimens three layers of denticles occur and 

 the individuals of the overlying layers alternate with those of the 

 underlying. The denticles are smooth, semicircular to hexagonal 

 in outline, irregular in size, have thin walls, and are strongly con- 

 cave from below. 



VALUE OF PALEOZOIC FISHES IN CORRELATING STRATA 



Fish remains have been used very little in exact correlation of 

 formations, but they should be of high value for such purposes. 

 As fishes swim freely and as few have their habitat determined by 



1 Geo!. Surv. Ill, VI, PL XX, Fig. 1. 



