I 



1850.] 121 



ing by the more prominent extremity of the organ to that part of the interior pa- 

 rietes of the cell, corresponding to the free surface of the animal upon which they 

 are placed. Their developement is special from the granular contents of the or- 

 ganic cells and not from the nucleus, for in the first or largest form of nettling 

 organs, in their developement upon a bud of the Hydra, I have been able to detect 

 one within an organic cell, and a nucleolated nucleus at its side. 



The foregoing observations have been made in frequent efforts to detect some 

 form of cell within the head of the Hydra which would be different from the gene- 

 ral structure of the body, and probably characterize a nervous system, but although 

 I have examined the animal in different menstrua under a variety of circum- 

 stances, I have never been able to discover anything which could be referred to a 

 nervous structure. 



December 17th. 

 Dr. Morton, President, in the Chair. 



A communication was read from the American Philosophical So- 

 ciety, dated Dec. 7th, 1850, acknowledging the reception of Part 1, 

 Vol. 2, of the Journal of the Academy. 



A communication was read from Dr. T. C. Henry, dated Albany, 

 Dec. 2d, 1850, in reference to two fishes from Oswego Lake, lately 

 presented by him to the Academy, and describing one of them as a 

 new species under the name of Centrarchus Oswego. On motion, the 

 communication was referred to a committee consisting of Mr. Cassin, 

 Dr. Fisher arid Dr. Leidy. 



Dr. Leidy presented for the inspection of the members, fragments 

 of fossil mammalian remains, from Missouri Territory, received from 

 the Smithsonian Institution, through Prof. Baird, consisting of portions 

 of crania, maxilla) and teeth, which he characterized under the names 

 of Rhinoceros nebraskensis a species not much larger than a common 

 hog, Palaeotherium Bairdii, Merycoidodon Culbertsonii, and Agrio- 

 choerus antiquus. 



1. Rhinoceros Nebraskensis. A species founded upon a great portion of the 

 face, containing all the superior molar teeth ; an inferior maxilla with six 

 molars ; and three superior, apparently deciduous molars. It is about the same 

 size as the R. minutus of Cuvier. 



Length of line of seven superior molars, .... 4 7-10 inches. 



" six inferior " . . . . 4 2-10 " 



Breadth of jaws from the first superior true molar teeth of one 



side to the other, 3 8-10 " 



2. Agriochcerus, n. g. Founded upon a great portion of the face and inferior 

 maxilla, containing six molar teeth on each side, and the posterior two molars of 

 both sides superiorly of another individual. The posterior molars of this genus 

 resemble in general form those of Merycopotamus, Fall-., 4- Cant., and are about 

 one-third smaller, but the outer demicones are not separated to the base from 

 each other like the former, but are combined by a rounded column as in Hyo- 

 potamus bovinus. 



