1868.] MEETING OF THE AMERICAN ASSOCIATION. 301 



of Ctenacanthus, with the tail of one of these Selachians distinctly 

 preserved. This Dr. Newberry said was a great rarity, as the 

 soft, and even the cartilaginous parts of plagiostomous fishes had 

 usually disappeared, the teeth, spines, and dermal tubercles — the 

 only bony parts — alone remaining. The only similar case of 

 which he had any knowledge was the discovery of the tail and 

 fins of Chondostreus, in the Lias of Lyme Regis, England, and 

 the preservation of Thyalina in the Solenhofen slate. The 

 specimen shown was greatly older than these, being from the base 

 of the Carboniferous, and was the only figure that nature has yet 

 given us of the external form of these ancient sharks. This tail 

 was very heterocercal, had the form of the caudal fins of some 

 living sharks, and indicated a fish of seven or eight feet in length. 

 In the specimen exhibited, the vertebral column had entirely 

 disappeared, but the impressions of the spinous bones were 

 distinctly visible, those of the lower lobe of the tail being ossified 

 throughout. Dr. Newberry said that he hoped to gather data 

 from this collection for uniting teeth and spines, which, though 

 described under different names, were parts of one fish. 



On some new Fossil Sponges from the Lower Silurian ; 

 by Prof. 0. C. Marsh. — The author exhibited and described 

 some specimens of the new genus Brachiospongia, from the Lower 

 Silurian rocks of Kentucky. These sponges, of which a full 

 account will shortly be published by Prof. Marsh, differ widely 

 from all the species hitherto known, and are of great interest to 

 science. 



On the occurrence of Fossil Sponges in the successive 

 groups of the Pal/eozoic Series ; by Prof. Jas. Hall. — 

 This paper was an epitome of all that is known of the sponges of 

 the Silurian, Devonian, Carboniferous, and Permian formations. 

 Sponges with calcareous skeletons, and coral-like forms, were 

 among the earliest inhabitants of the earth, being found in the 

 Lower Silurian strata. In the Devonian age they were still 

 more abundant ; but from this period diminished in numbers, and 

 became more like the horny sponges of the present day. 



On the American Beaver; by Lewis H. Morgan, 

 Rochester, N.Y. — The Beaver appears to be rapidly becoming 

 extinct wherever civilization advances. It is still found, how- 

 ever, in certain localities, from Virginia to the parallel of 60 N. 

 lat., though most abundant in the Hudson Bay Territory. Mr. 

 Morgan had examined the dams constructed by them around the 



