On the Structure 0/ Amphicentrum grarmlosum. 273 



EXPLANATION OF PLATE VII. 



Fig. 1. Thamnograptus Doveri, Nich., of the natural size. 



Fig. 2. A slab with numerous individuals of Azygograptus Lapworthi, 

 Nich., of the natural size. 2 a. A large individual of the same, 

 magnified two diameters. 2 b. Small portion of the base of the 

 same, enlarged still further. 2 c. A few cellules of the same, 

 greatly enlarged. 



Fig. 3. Didymograptus gibbertdus, Nich., of the natural size. 3 a. Base of 

 another specimen of the same, greatly enlarged. 3 b. Base of 

 another example of the same, with a spiuiform extension of 

 the sicula, greatly enlarged. 



Fig. 4. A specimen of Tetragraptus bryonoides, Hall, in which only two 

 of the four normal stipes are preserved. The two missing stipes, 

 not being in the same plane, are shown in outline. 



Fig. 5. Base of two of the stipes of Tetragraptus bryonoides, introduced 

 for comparison with the base of Didymograptus gibberidus, 

 greatly enlarged. 



XXXVI. — On the Structure of Ampliicentram grarmlosum, 

 Huxley. By Ramsay H*. Traquair, M.D., F.G.S., 

 Keeper of the Natural-History Collections in the Edin- 

 burgh Museum of Science and Art. 



[Plate IX.] 



Since Amphicentrum granulosum, Huxley, was first described 

 by Professor Young of Glasgow*, a second species, A. striatum, 

 has been recognized from the Northumberland coal-field by 

 Messrs. Hancock and Attheyf. Regarding the structural 

 peculiarities, however, of this most singular genus of Carboni- 

 ferous fishes, there has been nothing further published than 

 what is contained in Dr. Young's well-known paper "On the 

 affinities of Platysomus and allied genera." 



In a subject beset with such difficulties as the osteology of 

 fossil fishes, where the remains are, for the most part, either 

 crushed or fragmentary, it is natural that the advent of fresh 

 material should not only add to our knowledge but also reveal 

 errors in the descriptions of previous Avriters. And with 

 regard to Amphicentrum granulosum, the careful study of a 

 beautiful series of specimens from the North- Staffordshire 

 coal-field, recently lent me by my friend Mr. Ward, of Longton, 

 has led me to results which, in some important points, differ 



* Quart. Journ. Geol. Soc. vol. xxii. (1866), p. 306 ct seq. 

 t Ann. & Mag. Nat. Hist. ser. 4, 1872, vol. ix. p. 255. 



