494 Geological Society. 



the fiu 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 to 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 a memoir 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 Bridge water Treatise, PI. 10. 



