236 
ACTINOPTERYGII. 
1851. Gyrodus frontatus, A. Wagner, Abh. k. bay. Akad. Wiss., math, 
phys. Cl. yoI. vi. pp. 29, 55. 
1851. Gyrodus gracilis = “ Microdon hexagonus ,” A. Wagner, ibid. p. 32. 
(P) 1852. Gyrodus medius, F. A. Quenstedt, Handb. Petrefakt. p. 211, 
pi. xvi. fig. 2. [Imperfect fish ; Tiibingen University Museum.] 
1862. Gyrodus macrophtbalmus , A. Wagner, ibid. vol. ix. p. 336 (in 
part). 
1862. Gyrodus gracilis , A. Wagner, ibid. vol. ix. p. 338. 
1881. Gyrodus macrophthalmus, B. Vetter, Mittheil. k. mineral.-geol. 
Mas. Dresden, pt. iv. p. 20 (in part). 
1887. Gyrodus frontatus, K. A. von Zittel, Handb. Palseont. vol. iii. 
p. 242, fig. 254. 
1893. Gyrodus f rontatus, H. E. Sauvage, Bull. Soc. Hist. Nat. Autun, 
vol. vi. p. 440. 
Type. Nearly complete fish ; British Museum. 
A species resembling G. hexagonus in form and proportions, but 
differing in having the tubercular ornament of the scales, without 
reticulations, extending over the ventral half of the fish. 
The reticular ornament of the scales in Gyrodus evidently results 
from the connection of scattered tubercles by slight ridges. Such 
a modification may be produced during the growth of the fish, and 
in that case the so-called Gyrodus gracilis is probably the young 
stage of G. macrophthalmus and G. hexagonus as well as that of 
G. frontatus. 
Form. Sf Loc. Lower Kimmeridgian (Lithographic Stone): Bavaria, 
and Ain, France {Sauvage). 
P. 2096. Type specimen; Kelheim. Little can be seen of the 
scale-ornament of the ventral half of the fish, but the 
few traces remaining exhibit scattered tubercles without 
reticulation. Egerton Coll. 
22515. Remains of a smaller specimen ; Solenhofen. 
Purchased , 1848. 
P. 3770. Pish originally about 0T15 in length, wanting the anterior 
half of the head and the caudal fin; Kelheim. The 
characteristic expansions on the neural and haemal spines 
of the caudal region are conspicuous, as described in the 
next specimen. Six or seven basal cartilages are observed 
in the lobe of the pectoral fin, which is covered with thin 
round scales. Enniskillen Coll. 
P. 2097. Pine specimen 0*075 in length, shown of the natural size 
in PI. XVI. fig. 2; Kelheim. The coarse tubercular 
ornament of the cranial roof is shown, while the hinder 
margin of the frontal (/>*.) and the boundaries of the 
