Ao. 1884. A NEW SPECIES, EDESTU8 MIRUS—HAY. 37 



the roader may consult the report on this county made b}' Prof. Frank 

 A. Wilder ^ and a report on Iowa coals by Mr. Henry Hinds in volume 

 19 of the same survey. I am informed by Mr. David Wliite, of the 

 United States Geological Survey, that the Des !Moines stage belongs 

 either to the uppermost Pottsville or to the basal Allegheny. This 

 means that the species here described lived in the earlier part of the 

 era during which the coal beds of the eastern half of the United States 

 were deposited. The type of E. minor found in Parke County, Indiana, 

 appears to have lived at about the same time. Edestus Tieinrichi is 

 found in coal mines that appear to have approximately the same 

 level as those mentioned, but are possibly a little higher in the series. 



It may be proper to note here that tliere is a specimen of E. Tiein- 

 richi in the collection of the Iowa State Historical Society at Des 

 Moines. It was found, at Mystic, Appanoose County, Iowa. 



There seems to be no certain evidence that any species of Edestus 

 occurs in the upper half of the " Coal Measures." 



The sharks that belonged to the genus Edestus must have presented 

 a singular appearance with their straight or bent tooth shafts pro- 

 truding from their mouths, especially the species E. vorax and E. 

 giganteus, in wliich these organs attained a remarkable size. Never- 

 theless the individuals of Helicoprion and Lissoprion were still 

 stranger objects, since each must have carried in front of the mouth 

 a pair of weapons resembling circular saws, each 9 or 10 inches in 

 diameter. Karpinsky's figure has seemed grotesque enough, but it 

 probabl}^ tells only half the story. It remains now for some one to 

 explain how the toothed whorls of Helicoprion were produced and 

 attached. That of the lower jaw must have formed its segments 

 above and in close contact with the symphysis of the lower jaw. At 

 the same time the earlier-formed end of the last turn must have lain 

 below the symphysis, with the apices of its teeth pointing toward this. 

 According to Karpinsky's figure, there was the space of only 15 mm. 

 between the apices of these teeth and the base of the shaft. The 

 ligaments joining the right and left members of the lower jaw may 

 be supposed to have passed in this space, besides the skin and the 

 tissue underlying the shaft. It is, on the other hand, possible to 

 believe that the shaft itself formed the bond of union between the 

 two jaws and that nothing but the skin intervened between successive 

 turns. A similar but more difficult problem confronts us in the case 

 of the upper whorl. It will not do to push the whorl out in front of 

 the snout, as Karpinsky has done, by makhig the younger part of 

 the spiral relatively straight, for its last turn would stand out far from 

 the preceding ones, and of this there is no evidence or probability. 

 Besides, there would have been the same demand for a little curved 

 portion while the first turns were being formed. The determination 



> Geol. Surv. Iowa, vol. 12. 



