A94 Geological Society. 
the fin of a fish, and more fully justifying the propriety of the name 
Ichthyosaurus. Traces are also preserved of scutiform compart- 
ments on the integument of the fin. It is singular that this struc- 
ture should never have been observed in any of the numerous spe- 
cimens from Dorset and Somerset that have come under our notice ; 
whilst at Barrow-on-Soar, from whence the paddle in question was 
derived, even the fibres of the skin and folds of the epidermis are 
sometimes accurately retained*. 
Mr. Owen’s first part of his report on fossil Saurians, read at the 
British Association at Birmingham in August last, forms the com- 
mencement of a most important addition to the history of extinct 
reptiles. His recent investigations in Odontography have also sup- 
plied tu the geologist a new and most efficient instrument of investi- 
gation, enabling him to distinguish genera of extinct animals by the 
microscopic structure of their teeth ; and as, of all fossil remains, the 
teeth are the parts most perfectly preserved, and in the case of cartila- 
ginous fishes the teeth and spines are generally the only parts that 
have escaped decomposition, this method assumes an especial im- 
portance in fossil Ichthyology, as affording exact characteristics 
of animals long swept from the surface of the earth, and whose very 
bones have been obliterated from among the fossil witnesses of the 
early conditions of life upon our planet. By this microscopic test 
applied to the family of Sharks, Mr. Owen has confirmed the views 
of Agassiz respecting the affinities between the living Cestracion and 
the extinct genera Acrodus, Ptychodus, Psammodus, Hybodus, Co- 
chliodus ; in the case of animals also of the higher orders, he has 
settled the much-disputed places of several extinct gigantic Mam- 
malia by the same unerring test. Thus he has shown the supposed 
reptile Basilosaurus to be a Cetaceous mammifer, allied to the Du- 
gong; the Megatherium to be, as Cuvier had considered it, more 
nearly allied to the Sloth than to the Armadillo; and the Sauro- 
cephalus to be, as Agassiz had supposed it, an osseous fish. 
Dr. Malcolmson, in amemoir on the Old Red Sandstone of the north 
of Scotland, has done important service in showing that the rocks 
composing that group are divided into three formations, the two 
lower of which are clearly distinguished from each other by their 
fossil fishes. The cornstone or central formation is charged with 
numerous remains of Ichthyolites, including Holoptychus nobilis- 
simus, a new species of Cephalaspis, and other forms not yet de- 
scribed. The lower division, consisting in this region of conglome- 
rates, shales and sandstone, is characterized by the genera Dipterus, 
Diplopterus, Cheiracanthus, &c., of Agassiz, as well as by the 
occurrence of a singular Ichthyolite, which seems to offer close 
analogies to certain forms of Crustacea. By help of these Ich- 
thyolites, the author has been enabled to connect certain strata of 
Orkney and Caithness, and determine their relations to the beds of 
Old Red Sandstone containing fossil fishes in the basin of the Tay, 
and in the border counties of England and Wales, where they had 
been described by Mr. Murchison. 
* See Buckland’s Bridgewater Treatise, Pl. 10. 
