Leidy.] ^"^ [Nov. 18, 



In conclusion I would remark the fact that the gradual approaches in 

 character to the Bovidas by the recent and extinct genera and families, 

 furnishes one of the most admirable illustrations of the law of progressive 

 specialization by evolution known to me. 



Note. — Pi'ofessor Gill has presented in his system of the Mammalia 

 some reasons why the Suidoe should be more exactly defined than I have 

 given above. In the Suina? and Phaochoerin* the postglenoid process is 

 wanting or rudimental, and the mandibular condyle is flat and triangular. 

 In the Dicotylinaj and Hippopotaminai the postglenoid process is well de- 

 veloped and the condyle is subcylindric, as is also the case in Elotherium. 

 I therefore place the two subfamilies named in a family separate from the 

 Suidfe, under the name Hippopotamidae, to which it is possible that Elo- 

 therium should be united as a third subfamily. 



Biographical Notice of Isaac Lea, LL.D. By Josepli Leidy, M.D., LL.D. 

 {Read before the American Philosophical Society, November IS, 1SS7.) 



In accordance with the custom of this Society, which requires that a 

 record shall be made of the claims of its deceased members to remem- 

 brance, at the request of our President, I have prepared a brief sketch 

 of one who was distinguished among us, our late much respected fellow- 

 citizen and friend, Isaac Lea, LL.D. A more detailed memoir than the 

 one I offer seemed supererogatory from the fact that only a short time 

 previous to his death, there was published in the Bulletins of the United 

 States National Museum, a volume containing a Biographical Sketch of 

 Mr. Lea, comprising fifty-nine pages ; and a Bibliography of his publica- 

 tions with a synopsis of the material therein contained, comprising 278 

 pages, prepared at the request of the Smithsonian Institution, by Mr. N. 

 P. Scudder. To this source I have conveniently applied for much of the 

 information of my notice. 



Isaac Lea was born March 4th, 1792, in Wilmington, Delaware. His 

 grandparents, John and Elannah Lea, came from Gloucestershire, Eng- 

 land, and accompanied William Penn in his second visit to this country. 

 They were members of the Society of Friends, among whom they were 

 noted as ministers. The father, James Lea, was a merchant, and at the 

 age of fifteen Isaac went to Philadelphia to engage in a similar pursuit. 

 In 1814, the country being at war with England, Isaac joined a volunteer 

 'rifle company, which oftered its services to the Governor of the State in 

 case of need. As the services were not required, the company was soon 

 disbanded ; but in consequence of Isaac joining it, he lost his birthright 

 in the Society of Friends. 



At an early age Isaac showed a love for natural history, in which he 

 was encouraged by his mother, who was herself fond of botany, and in- 



