NATURAL SCIENCES OP PHILADELPHIA. 267 



of the wood. Thus in the case of the strong shoots which in 

 this country formed the ultimate trunk of the Paulownia impe- 

 rialism the pith occupied a space in the centre of from one-quarter 

 to three-quarters of an inch in diameter according to the strength 

 of this shoot; but in some trees about twenty-five years old, he 

 had seen cut down, the pith cavity was nearly obliterated. It was 

 scarcely credible that any dicotyledonous shoot of one year's 

 growth ever had a pith as thick as this. 



But besides these incongruities he had been able to trace the 

 origin of similar formations. In central New York, he had seen 

 on a farm a large number of hollow cylindrical substances from 

 one-quarter to one inch or more in diameter which appeared like 

 pieces of large clay pipe stems. There were many successive cir- 

 cular layers as in this specimen. Informed by the farmer that 

 they came in the muck obtained from a swamp near by, he examined 

 the spot, and found in many instances the central portion was 

 occupied by decaying wood and roots. In time these rotted com- 

 pletely away, and left the structure a hollow tube. The mineral 

 substance around this woody matter appeared to be carbonate of 

 lime, and as the swamp was very wet. in winter, and partly dry in 

 summer, he supposed the varying temperature of the water at dif- 

 ferent seasons of the year, or perhaps actual periodical dryness, 

 would give the appearance of annual rings to the deposit, which 

 formed around the woody core. 



He would suggest that probably this piece had been formed in a 

 similar manner, and that after the woody centre which had formed 

 the nucleus of the cylindrical mass had decaj^ed and disappeared 

 through the ends, the crystallized silicious matter had formed in 

 its place. 



Notice of Donation of Fossils, etc., from Wyoming. Prof. Leidy 

 directed attention to the specimens of fossils and other specimens 

 from Wyoming Territory, presented this evening. 



The fine specimen consisting of a nearly complete dorsal shell 

 of a Trionyx, was found on the buttes of Dry Creek, about ten 

 miles from Fort Bridger. It was discovered by Maj. R. S. La 

 Motte, commander of the fort, and was kindly presented by him 

 to the Academy. The shell is about 16^ inches long and nearly 

 as broad. Before comparing it with the specimen of Trionyx gut- 

 tatus it was supposed to be the same, but certain characters ap- 

 pear to indicate it as a distinct species, which may be named Trio- 

 nyx uintaensis. The fore and back parts of the carapace are trun- 

 cated as in the existing T. muticus. The back truncation is slightly 

 sinuous, and extends the width of the last two pairs of costal 

 plates. In T. guttatus the corresponding border is convex and 

 exhibits a deep median and two deep lateral sinuses. The speci- 

 men possesses only six pairs of vertebral plates. 



Of the other fossils a number pertain to a large land tortoise, 



