FLOOR.] 
FOSSILS. 
173 
Over Case 6 are placed the silicified stems of Mantellia, plants 
related to the recent Cycas, and called "petrified crows' nests" by the 
Portland quarrymen. 
The Table Case under the window contains leaves of Dicotyledonous 
Plants, from the Miocene "Brown-Coal" of Germany; the Tertiary 
Limestone of CEningen; from Mackenzie River; Greenland, &c. In the 
next Case are the Tertiary Plant-remains from Grinnell Land brought 
home by H.M. ships " Alert " and " Discovery " from lat. 81° 45' N. 
The slabs of Sandstone on the North Wall of this Room, on the 
left, with the tracks of an unknown animal, called Cheirotherium, 
probably amphibious, with large hind feet, like some Batrachians, 
are from the quarries of Hildburghausen, in Saxony. On the right 
hand are placed slabs also supposed to be of the New Red Sandstone 
formation, with equally remarkable impressions of various dimensions, 
called Ornithichnites, being regarded as the foot-marks of birds. They 
occur in the Sandstone beds near Greenfield, Massachusetts, atTurners 
Falls, in the Connecticut River. Other slabs from the same locality, 
and also from Cheshire and Staffordshire, covered with reptilian 
footprints, are placed on Wall Cases 1 and 1 1 of Room III. and in 
the third window recess of Room II. On the North Wall of Room I. 
are Plant remains from Solenhofen, in Bavaria. 
ROOM II. 
The classification of the Fossil Fishes, arranged in this room, is 
chiefly in accordance with that proposed by M. Agassiz, in his great 
work, entitled "Recherches sur les Poissons Fossiles, " with some mo- 
difications founded upon the later systems proposed by Professors Miiller 
and Owen. The series commences with the Placoid Fishes, or those of 
the Shark and Ray tribes, in which the skin is protected by rounded 
(often star-shaped) and very hard scales, having frequently a raised 
point, and sometimes a thorn-like prickle in the centre, as may be 
seen in the scales of the Thornback and some other fishes of the 
Skate tribe. The upper division of the tail is prolonged beyond the 
lower lobe, and is supported by a continuation of the vertebral 
column — a form of tail which is termed Hetero cereal, and which is 
most commonly found in all the orders of fishes of the middle and older 
Geological formations ; but which (if we except the Sharks and Rays) 
is rarely met with in the existing species of fishes, in which the " ho- 
mocercal " tail, or that with the two lobes equal, prevails. 
The skeleton of the Placoids being more or less gristly or cartila- 
ginous, and in the same degree perishable and incapable of fossilization, 
the remains of those fishes consist chiefly of the defensive spines, 
scales, and teeth ; these objects, being mostly of small size, will be found 
in the Cases under the windows, and in Case 7 at the end of the room. 
The Fishes called Ganoids have derived their name, and the 
character of their order, from the lustre of their very hard, enamelled 
scales ; and it is by these parts that they are chiefly represented in 
the fossil state. The most common form of scale in this order is the 
