90 [Oct. 



Also a letter from the Linnean Society of Lyons, dated July 1, 

 1850, presenting the Annals of that Society for 184.7-49. 



A letter was also read from J. A. Grex, Esq., addressed to the Libra- 

 rian, dated New York, October 3, 1850, transmitting the above works, 

 and acknowledging the reception of a copy of the Journal, Vol. 1, new 

 series, and of a copy of the Proceedings, for the Agricultural Society 

 of Lyons. 



Dr. Leidy presented two papers, one describing two new species of 

 Infusorial Entozoa, and the other entitled "descriptions of somenema- 

 toid Entozoa infesting insects," both of which were referred to the 

 committee having charge of previous communications by Dr. Leidy 

 read at late meetings of the Society, viz., Drs. Hallowell, Keller, and 

 Zantzinger. 



Dr. Leidy also made the following observations on two new genera 

 of mammalian fossils, which he designates under the names of Eucro- 

 taphus Jacksoni, and Archaeotherium Mortoni : 



The two fragments of mammalian crania, which I exhibit this evening to the 

 Academy, are part of those specimens a short time since presented to our Cabinet 

 by Mr. Joseph Culbertson, of Cumberlandj Co., Penna., whose son obtained 

 them from that region of country, in the vicinity of Fort Laramie on the Platte 

 river, known as the " mauvais terres," or " bad lands," a locality, which, 

 according to recent researches made by Dr. John Evans, is rich in such 

 remains. Both fragments belong to new genera of mammalia. The smaller 

 of these I have named Eucrotaphus, on account of the comparatively very large 

 size of the temporal bones. It consists of the central portion only of the cranium, 

 and is a little longer than the corresponding portion of the skull of the beaver 

 (Castor fiber.) In general outline it resembles the posterior part of the cranium 

 of the American mink, (Mustela lutreola) or more particularly that of the opos- 

 sum, (Didelphis virginiana;) being broad posteriorly, cylindroid anterior to the 

 ossa tempora, but is not as bulging at the sides as in the latter mentioned 

 animals. 



The boHes still existing in the specimen consist of the right temporal, except 

 its zygoma and posterior superior portion ; a portion of the left squamous bone ; 

 the middle portion of the ossa parietalia, ossified into one, except the sagittal 

 crest ; the right para-mastoid, or paroccipital process, except the tip, with a 

 small fragment of the occiput above it ; the posterior sphenoid, somewhat 

 mutilated ; a fragment of the presphenoid ; and a fragment of the basioccipital. 



The most remarkable characteristics of this head are: first, the comparatively 

 enormous size of the squamous portion of the ossa tempora; second, the great 

 advancement of the ossa parietalia ; * third, the deep groove in the ossa parietalia 

 iust in advance of the squamous suture ; fourth, the strength of origin of the 

 zygoma ; and fifth, the form of the glenoid cavity. 



I for some time hesitated before I applied this name to the symmetrical bone 

 occupying the upper part of the cranium. I thought at first it was the frontal 

 extending very far back, but upon considering the advanced position of the squa- 

 mous portion of the temporal bone, and observing in the Erinaceus ecaudatus, 

 a considerable prolongation forward of the ossa parietalia, I concluded that it 

 belonged to the latter category. 



