VERTEBRATES. 353 



On comparing the specimen under consideration with that described by Prof. 

 Leidy, it will be seen that ours is less robust ; that the segments overlap to a 

 much greater extent; that the denticles are broader, not so high, and are not 

 set obliquely on the spine as in E. vorax, while the decurrent spur of the 

 enameled base is much longer and more acute. 



From the specimen exhibited to the Am. Ass. by Prof. Hitchcock, and which 

 is probably identical with that described in this report, vol. ii, p. 84, as E. mi- 

 nor, N., the one before us may be distinguished by its greater size, its more 

 rectilinear outline having only one of its margins curved and by its shorter, 

 broader and more erect denticles. 



The specimen of E. vorax described by Prof. Leidy, is supposed to have 

 been found in the Coal Measures of Western Arkansas, was coated with car- 

 bonaceous matter, and was doubtless taken from a stratum of cannel or bitumi- 

 nous shale. 



Prof. Hitchcock's specimen was obtained from a layer of " slate " (Bitumi- 

 nous shale ?) which overlies a seam of coal in Parke Co., Indiana. 



The specimen described in the 2d vol. of this report was obtained from a bi- 

 tuminous limestone in Posey Co., Indiana ; while that before us is reported by 

 Mr. Heinrich to have been found in the coal of Belleville, Illinois. 



In all these cases, the enclosing material was undoubtedly an aqueous sedi- 

 ment, as the bituminous shales interstratified with the coal seams and cannel 

 beds always are. There is, therefore, no reason to doubt that the animal which 

 bore this organ was aquatic in habit.* 



The species described above is dedicated to Mr. John P. Heinrich, in whose 

 mine it was found, and to whose intelligent appreciation of its scientific value 

 we owe its preservation, as to his courtesy we are indebted for the opportunity 

 of describing it. 



*In the Am. Jour Sci. 2d series, vol. xxiii, p. 212, will be found a discussion of the origin 

 of the difference between cannel and ordinary bituminons coal. The conclusion drawn from 

 the facts there cited is that this difference is mainly due to the relative quantities of water 

 present during the process of bitumization; cannel coal having been formed from vegetable 

 matter completely submerged, while ordinary bituminous coal was produced from vegetable 

 matter saturated, but not constantly covered with water. In the former case, the vegetable 

 tissue was thoroughly macerated, its softer parts forming a fine carbonaceous pulp which was 

 suspended, transported and deposited in laminated beds by water action. All cannel coals 

 may be said to contain remains of fishes, shells, or aquatic reptiles, while ordinary bitumi- 

 nous coal rarely contains anything but vegetable organisms. In the open lagoons of peat 

 bogs which receive the leachings of the surrounding mass of vegetable matter, and where a 

 fine carbonaceous mud is deposited with the remains of aquatic animals cannel may be said 

 to be forming, while the spongy, saturated, but not submerged peat, may be regarded as the 

 representation of our cubical coals. 



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