148 Dr. C. It. Eastman — New Form of Shark's Dentition. 



The great inequality and difference of shape of the opposite valves 

 ascribed to the same species are also characteristic and peculiar 

 features. 



EXPLANATION OF PLATE VII. 



Fig. 1. — Trochoceras spurium, Salter (« 466). Wenlock Shale: Builtli Bridge. 



Drawn nat. size. 

 Fig. 2. — Ortlioceras fiuctuattmi, Salter {a 611). Lower Bala (Llandeilo) : Wellfleld, 



Builth. X twice nat. size. 

 Fig. 3. — Pterinea exasperata, Salter («. 816). Wenlock Limestone: Dudley. 



X Ik nat. size. 

 Fig. 4.— Ditto "(« 813). 



Fig. 5. — Ditto \a 816), 4 ribs enlarged 4 times nat. size, to show ornamentation. 

 Fig. 6. — Fterinea condor, Salter (« 809). Lower Ludlow Beds: Dudley. Left 



valve. ' Nat. size. 

 Fig. 7. — Ditto, right valve {a 810), nat. size. 



II. — On Campylopbion, a. New Form of JEdestus-'lik.t^ Dentition. 



By Dr. C. E. Eastman, of Cambridge, Mass., U.S.A. 



(PLATE VIII.) 



IN the January number of the Geological Magazine for 1886, 

 an elaborate description is given by Dr. Henry Woodward of 

 a peculiar ichthyic structure from the Carboniferous of Western 

 Australia, which is referred by him provisionally to Edestus, under 

 the specific title of E. davisii. Interesting comparisons are drawn 

 between this and other known species of Edestus, and the hypothesis 

 advanced that it is a pectoral fin-spine, resembling in its segmented 

 character the Cretaceous Pelecopterus. This segmentation, which 

 is so conspicuous a feature of Edestus, is attributed by Dr. Bashford 

 Dean in his book on "Fishes, Living and Fossil," to a metameral 

 origin, and he follows Leidy, Owen, Cope, Newberry, and others 

 in interpreting all this class of remains as dorsal fin-spines. 



As early as 1855 Louis Agassiz ^ compared the type-specimen 

 of Edestus minor, Newberry, with the rostral pi'olongation of Pristis, 

 and pronounced it a dermal defence, pertaining probably to the 

 snout region of a shark or skate. Quite recently this hypothesis 

 has been revived by Dr. A. Karpinsky, Director of the Eussiau 

 Geological Survey, in his superb memoir on Helicoprion,'^ a spirally 

 coiled form whose segments resemble those of Edestus, and is 

 regarded by the author as a powerful weapon placed above the snout 

 in the median line. To this Permo-Carboniferous genus, Helicoprion, 

 the Eussian Director also refers the Australian form described by 

 Dr. Henry Woodward as Edestus davisii, which differs principally 

 in the lesser extent of its spiral. In an appreciative review of his 

 monograph. Dr. Arthur Smith Woodward^ questions the probability 

 of Karpinsky's conjecture, and cites a recent discovery made by 

 Dr. Traquair in the Lower Devonian of Forfarshire, which " proves 



1 Proc. Amer. Assoc. Adv. Sci., 1855 (1856), p. 229. 



'^ Verh. k. russ. min. Ges. St. Petersburg, 1899, ser. ii, vol. xxxvi, No. 2. 



3 Geol. Mag., 1900, Dec. IV, Vol. VII, p. 33. 



