226 
ACTINOPTERYGII. 
P. 4694. Imperfect fish, displaying the expansion at the inferior 
end of the problematical bone (? ridge sente) at the hinder 
extremity of the body-cavity ; Cirin. Purchased , 1884. 
Microdon egertoni (Thiolliere). 
1854. Pycnodus egertoni , V. Thiolliere, Poiss. Foss. Bugey, pt. i. p. 24, 
with figure. 
1856. Microdon egertoni , J. J. Heckel, Denkschr. k. Akad. Wiss. 
math.-naturw. Cl. vol. xi. p. 201. 
1860. Microdon egertoni , A. Wagner, Gelehrte Anzeig. k. bay. Akad. 
vol. 1. p. 896. 
Type. Nearly complete fish ; Lyons Museum. 
A small form of Microdon , not yet satisfactorily distinguished 
from the type species. It is stated to differ in not exhibiting an 
angulation of the frontal profile and in having fewer vertebrae : 
but the first character may be due to imperfect preservation, and 
the second is difficult to observe with certainty. 
Form. Sf Loc. Lower Kimmeridgian (Lithographic Stone) : Ain. 
France. 
P. 1637. Imperfect, crushed specimen 0-13 in length, shown for 
the most part in impression ; Cirin. Egerton Coll. 
P. 4695. Slightly larger specimen displaying the pelvic and median 
fins, but wanting the greater part of the head ; Cirin. 
Purchased , 1884. 
Microdon sauvanausi (Thiolliere). 
1850. Pycnodus sauvanausi, V. Thiolliere, Ann. Soc. Sci. Phys. & Nat. 
Lyon, [2] vol. iii. p. 131. 
1854. Pycnodus sauvanausii , V. Thiolliere, Poiss. Foss. Bugey, pt. i. 
p. 15, with plate. 
1856. Microdon sauvanausii, J. J. Heckel, Denkschr. k. Akad. Wiss., 
math.-naturw. Cl. vol. xi. p. 201. 
Ti/pe. Nearly complete fish; Lyons Museum. 
A large species attaining a length of about 0-6. Maximum depth 
of trunk apparently equalling about half of the length of the head 
and trunk without caudal fin; head with opercular apparatus 
occupying somewhat more than one-quarter of the total length of 
the fish. Each premaxilla with two chisel-shaped teeth; [other 
teeth imperfectly known]. Scales apparently confined to the most 
anterior part of the trunk. 
A fish from Cirin described as intermediate between this and the 
