36 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.42. 



preceding it. Furthermore, since the trouglilike tooth bases last pro- 

 duced are much shorter than the older ones, it must be that the latter 

 continued for a long time to grow backward. This resulted in main- 

 taining and increasing the size and the strength of the shaft. 



As stated, the base of the crown of each tooth is prolonged back- 

 ward. Now if we apply this rule to the tooth masses of Helicoprion 

 and Lisso'prion, we are led to the absurd conclusion that the very 

 small teeth of the innermost coil are the ones that were last formed. 

 The same remark will apply to Toxoprion. It becomes evident,, 

 therefore, that there existed some important differences, other than 

 that of form, between Edestus and the genera just named. 



As will be seen from the figures, many small particles are scattered 

 over the block below the lower shaft. These appear to consist mostly 

 of particles of decayed calcified cartilage, but there appear to be 

 occasional scales of shagreen. Here also are seen two teeth which 

 Doctor Eastman, on examining the specimen, recognized as belong- 

 ing to the Orodus type. It is possible, not to say probable, that 

 these teeth were originally attached to one of the jaws of the Edestus. 

 If they were a part of the armature of Edestus, this fact would go 

 far toward confirming Doctor Eastman's belief that Edestus had 

 been derived from some form like Orodus or Cwmpodus. It might 

 be that from a shark having in the upper or the lower jaw two rows 

 of symphysial teeth there might arise a form having but one row, 

 enlarged and especially modified tlu-ough the reduction of the other 

 row of the pair. Something like this is seen in the usually unpaired 

 and greatly developed canine tooth of Monodon. In assigning these 

 Orodus-Wko. teeth to the jaws we must consider the fact that the 

 teeth- indicated on plate 1 by the numerals 11 and 12 probably 

 belong on the upper jaw. 



The remains here described appear to represent a species hitherto 

 unknown. It closely resembles Edestus minor Newberry. It differs 

 from the latter in having the tooth shafts more strongly bent and in 

 having the apices of the teeth more acuminate. In E. minor, as in 

 the present species, the front border of each tooth is convex, but the 

 hinder border is either nearly straight or only slightly concave for most 

 of the length, while near the apex it becomes convex. In the new 

 species the whole posterior border is concave and the apex of the tooth 

 is relatively slender. It appears also that the denticulations of the 

 teeth of E. minor are at right angles with the border, while in the 

 present species they are directed distinctly toward the apex. 



I propose to call the species represented by the above-described 

 remains from Lehigh, loAva, Edestus mirus. 



As already stated, tliis specunen was found in the black shale over- 

 lying the Tyson seam. This seam belongs to the Des Moines stage of 

 the " Coal Measures." For details regarding the geology of this region 



