234 
ACTINOPTEKYGII. 
depth of trunk not exceeding its length from the scapular arch to the 
base of the caudal fin, and head with opercular apparatus occupying 
one-third of the total length exclusive of the caudal fin. [Dentition 
unsatisfactorily known hut] principal teeth exhibiting two crimped 
rings on crown. Dorsal fin occupying the hinder half of the hack, 
and its maximum elevation equalling about one-fourth of the depth 
of the trunk at its insertion. Scales towards the dorsal margin 
conspicuously tuberculated, the others marked with a coarse reticu¬ 
lation. 
Form. Sf Log. Lower Kimmeridgian (Lithographic Stone): Bavaria. 
P. 1620, P. 3771. Nearly complete fish 0‘19 in length, partly in 
counterpart, wanting the greater part of the dorsal and 
anal fins ; Kelheim. Egerton and Enniskillen Colls. 
P. 3766. Portion of trunk of a large fish, probably of this species; 
Kelheim. Enniskillen Coll. 
P. 1621. Imperfect anterior portion of small fish, probably of this 
species ; Kelheim. Egerton Coll. 
Gyrodus hexagonus (Blainville). 
[Plate XVI. fig. 3.] 
1818. Slromateus hexagonus, H. D. de Blainville, Nouv. Diet. d’Hist. 
Nat. vol. xxvii. p. 334. 
1833-44. Microdon hexagonus, L. Agassiz, Poiss. Foss. vol. ii. pt. i. 
p. 16, pt. ii. pp. 184, 206, pi. lxix. c. figs. 4, 5. 
1833-44. Microdon analis, L. Agassiz, ibid. pt. i. p. 16, pt. ii. p. 207, 
pi. lxix. c. tig. 3. [Nearly complete fish; Palaeontological Museum, 
Munich.] 
1844. Gyrodus analis, L. Agassiz, ibid. pt. ii. p. 300. 
1851. Gyrodus hexagonus, A. Wagner, Abh. k. bay. Akad. Wiss., 
math.-phvs. Cl. vol. vi. pp. 32, 40, 44, pi. iii. fig. 1. 
1851. Gyrodus lepturus, A. Wagner, ibid. vol. vi. pp. 31, 56. [Imperfect 
fish ; Palaeontological Museum, Munich.] 
1852. Gyrodus inigosus, F. A. Quenstedt ( errore ), Handb. Petrefakt. 
p. 211, pi. xvi. fig. 1. 
1862. Gyrodus hexagonus, A. Wagner, loc. cit. vol. ix. p. 334. 
1881. Gyrodus macrophthalmus, B. Vetter, Mittheil. k. mineral.-geol. 
Mus. Dresden, pt. iv. p. 20 (in part.) 
1887. Gyrodus hexagonus , K. A. von Zittel, Handb. Palaeont. vol. iii. 
p. 241, fig. 252. 
Type. Nearly complete fish and fragment; Palseontological 
Museum, Munich, and British Museum. 
A species, so far as known, closely similar to the type, only 
differing in the relatively greater protuberance of the abdominal 
