ACAXTHODIDiE. 
5 
The squamation appears to be of equal fineness over the whole of 
the trunk, there being no fulcral scales even on the upper caudal 
lobe ; while the only diminution in the size of the quadrate granules 
occurs in this region and towards the distal margins of the fins. 
The scales are either rectangular or slightly rhomboidal, with a flat¬ 
tened or faintly excavated external surface, usually smooth ; and 
their attached surface exhibits a gentle convexity. A single lateral 
line occurs high on each flank, marked not by any tubular or other 
excavation of the scales, but by the ridge-like displacement of two 
series, between which the organ originally extended. The supposed 
evidence of additional sensory canals appears to the present writer 
to be due to a misinterpretation of the displaced dorsal and ventral 
ridges, which exhibit no median series of scales. 
The evolution of the paired fins in the successive species of Acan- 
thodes, as defined below, is of some interest. In the Upper Devonian 
representatives of the genus the pelvic fins are not much inferior in 
size to the pectorals, and are placed nearly midway between the 
latter and the anal. In the Lower Carboniferous A. nitidus the 
pelvic fins are similarly placed, but reduced in size. In the Upper 
Carboniferous A. warcli the same fins are not only further reduced, 
but occupy a more forward position, while the pectorals are much 
enlarged. In the Lower Permian species the pelvic fins become 
insignificant and the pectoral fins enormous, while the two pairs are 
even more closely approximated than in the earlier forms. 
Acanthodes bronni, Agassiz. 
1832. Acanthoessus bronnii, L. Agassiz, Neues Jakrb. p. 149 
1833-35. Acanthodes bronnii , L. Agassiz, Poiss. Foss. vol. ii. pt. i. 
pp. 20, 124-, pi. i. 
1848. Hoi acanthodes gracilis , E. Beyrich, Monatsb. Beri. Akad. p. 24. 
1857. Acanthodes gracilis, F. Roemer, Zeitschr. deutsch. geoi. Ges. 
vol. ix. p. 65, pi. iii. 
1857. Acanthodes bronnii, F. H. Troschel, Verhandl. naturh. Ver. preuss. 
Rheinl. u. Westph. vol. xiv. p. 2, pis. i., ii. figs. 1-13. 
1861. Acanthodes gracilis, H. B. Geinitz, Dyas, p. 21. 
1864. Acanthodes bronnii, E. Weiss, Zeitschr. deutsch. geol. Ges. vol. 
xvi. p. 291. 
1868. Acanthodes bronnii and A. gracilis , R. Kner, Sitzimgsb. k. k. 
Akad. Wiss. Wien, math.-naturw. Cl. vol. Ivii. pt. i. p. 303, pis. 
v.-viii. 
Type. Imperfect fish; olim H. G. Brown Collection. 
The type species, attaining a maximum length of about 0*3. 
Body much elongated and slender, the maximum depth being con¬ 
tained about six or seven times in the total length. Pectoral fin- 
