pkesident's address. 10 



Unionid^ having existed as early as the Cretaceous and even the 

 Jurassic period. 



II. THE EURYG^AN OR EURASIATIC REALM. 



The European or Palaearctic Reahii is the largest of all, and 

 embraces the entire northern portion of the Old World. Its south- 

 ern limits nearly coincide with the tropic of Cancer in the lowlands, 

 and its isotherm projected therefrom in the more rugged countries. 

 In Africa it extends into the Desert of Sahara, and in Asia it is 

 limited by the Himalaya Mountains and their spurs. It possesses 

 members of 31 families of terrestrial mammals, 55 of birds (accord- 

 ing to Wallace), 25 of reptiles, 9 of amphibians (according to Giui- 

 ther), and 16 of fresh-water fishes. None of these families, how- 

 ever, are continuous over the entire area and at the same time pe- 

 culiar to it. It is true that several families are restricted within 

 its limits, such as the Trogonophid^e and Ophiomoridce among 

 reptiles, and the Comephoridse among fishes, but these are very 

 limited in their distribution; the family Comephoridse, ^. ^^'•., is 

 represented by a single species, confined to a single lake (Baikal) 

 of Siberia. The realm is characterized, therefore, rather by what 

 it has not than by what it has among families, and is based mainly 

 on the structural modifications of minor value (generic or specific) 

 of its constituents. 



III. THE INDOG^AN REALM. 



The Indian or Oriental Realm is of less extent than either of 

 the two preceding ones, but is nevertheless richer than either in the 

 number of species. It extends from the Himalayan range on the 

 north to the Indian Ocean on the south, and toward the S. E. is 

 limited by the narrow but deep strait which intervenes between 

 Celebes Island and its dependencies on the one hand, and Borneo 

 on the other, and also between the island of Lombok on the 

 cne hand and Bali on the other; it thus includes the penin- 

 sulas of Hither and Farther India, and the Indo-Malayan Archi- 



