121 REPORT 1884. 



permanently. However, this seems open to the same objection as the preceding' 



theory. 



Last come the Astronomical or Periodical theories. A tilt of the earth's axis 

 was suggested by Belt, but suggested as owing to causes which are wholly insuffi- 

 cient. Tilting from astronomical agencies is slight, though its action -would be in 

 the direction required. Herschel suggested the Eccentricity theory, but abandoned 

 it. Adhemar's Precession theory, as explained by himself, involved an absolute 

 fallacy. The celebrated view of Dr. Croll combines the Precession and Eccen- 

 tricity theories into one. It exactly agrees with the Antarctic greater extension 

 of ice, and provides an explanation "of interglacial warm periods. The great diffi- 

 culty in its way is to see how a mere difference in distribution through the year of 

 an unchanged total heat-receipt can produce consequences so vast. The laws of 

 radiation explain but a very minute part, the laws of evaporation perhaps rather 

 more ; but, so far as can at present be seen, both together are inadequate. Another 

 serious objection is that the theory seems to require the climate of the northern 

 hemisphere to be now in a state of change for the better, of which at present then* 

 appears no evidence. 



Dr. Croll's elaborate explanations of the reaction of one effect upon another — 

 fogs, deflection of currents, and the like — have no special connection with his 

 own theory. They would act in all cases, and support all theories equally. Tin- 

 arguments, if admitted, would only prove that the earth's climates are in a state of 

 hio-hly unstable equilibrium, in which a slight cause may produce an enormous 

 change. Nor are his arguments universally admitted. 



In conclusion, Dr. Croll's theory seems inadequate : alteration of currents and 

 winds are the most powerful causes suggested hitherto : further investigations 

 ought to be made as to the nature and extent of the last series of changes in the out- 

 lines of the continents of the globe. 



9. On the recent Discover// of nev and, remarbihL> Fossil Fislies in the 

 Carboniferous and Devonian Rocks of Ohio and Indiana. By Professor 

 J. S. Newberry, M.D. 



The fishes described by the author consisted of: — 



1. Two new species of Dinichthys from the Huron Shale (Upper Devonian) of 

 Northern Ohio. Of these one is considerably larger than either of the two gigantic 

 fishes described in the Geological Report of Ohio under the names of Dinichthys 

 Herzeri and D. Terrelli, the cranium having a breadth of 3 feet 8 inches. This is 

 about one-third larger than the largest specimen of Dinichthys before known, and 

 two or three times as large as Asterolepis of Hugh Miller and Heterostens of Pander, 

 its congeners. Another is a small species of Dinichthys of which the dorso-median 

 plate is only 5 inches in breadth and G in length. The mandibles are not more 

 than G to 8 inches in length, but are much worn by long use, indicating maturity. 



2. The pavement teeth of a gigantic ray, Archceobatis gigas, Newb., from the 

 lower Carboniferous of Indiana ; the largest tooth is over 6 inches long by 4 inches 

 wide and one and a half thick. These teeth formed several rows in the mouth 

 above and below. In shape they resemble the teeth of Psamodus, but the enamelled 

 surface was strongly ridged to prevent the slipping of molluscs, Crustacea, &c, 

 which formed the food of the fish. 



3. Diplognathus mirabilis, Newb., a new genus and species in which the man- 

 dibles, set along the anterior portion with conical teeth, diverge at the symphysis, 

 forming a foi'k which carries another row of strong, acute, recurved teeth. As 

 such a forked jaw would be liable to be split, the rami were united at the sym- 

 physis by a strong ligament, deeply inserted in each bone. This apparatus, 

 admirably adapted for catching slender and slippery fishes, is different from any- 

 thing hitherto known among vertebrates. 



4. The teeth of several species of Mylostoma, Newb., a new genus of fishes, 

 probably allied to Dinichthys on the one hand and to Ctenodus on the other, in 

 which the under jaw was provided with one or more pairs of powerful crushing 



