4 CO ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



water representatives are either exceptional or anadromous. 

 There are about twenty-five species, the families being the 

 Petromyzontids, Anguillids, Dorysomids, Clupeids, Microsto- 

 mids, Atherinids, Scia?nids, and Gadids; one family (the Cy- 

 prinodontids) is as much a salt-water as a fresh-water type; 

 the remaining two are either, as in the case of the Cyprinids, 

 purely fresh-water fishes, or, as in the case of the Silurids 

 (catfishes), while certain groups of genera are marine, others 

 exclusively affect the fresh water. 



Still more remarkable than the number of families peculiar 

 to the region in question is the number of genera. Accept- 

 ing the idea of genus current among American ichthyolo- 

 gists, certainly over 110 are confined to this region. Even 

 of the Cyprinids, which are more nearly equally diffused over 

 the northern hemisphere than any other family, most of the 

 genera are peculiar, and the only ones, apparently, common 

 to Europe and America are Telestes, jSqualius, Phoxinus, Leu- 

 cos, and Alburmis. It is to be remarked that the genera 

 shared in common are chiefly represented in America on 

 the Pacific slope, and thus corroborate the closer relation- 

 ships existing between that side of the continent and the 

 Old World. 



Vascular Dentine and Movable Teeth in Fishes. 



Mr. C. S. Tomes, the well-known authority on the teeth of 

 Vertebrates, has especially studied the structure and develop- 

 ment of vascular dentine, and has announced, as the result 

 of such studies, that there are four modifications, which are 

 distinguished by him in the following terms: 



(1) "Hard, unvascular dentine, the characters of which are 

 sufficiently known. 



(2) " Vaso-dentine, which is developed from odontoblasts 

 after the manner of dentine, but contains an anastomosing 

 net-work of canals modelled around and containing capillaries. 



(3) " Plici-dentine, developed from odontoblasts, but from 

 a complicated pulp, so that it is more or less divided up into 

 distinct systems of dentinal tubes. 



(4) " Osteo-dentine, developed from osteoblasts, like bone, 

 and quite unlike dentine, permeated by a system of large 

 canals, which do not contain, or have any special relation to, 

 blood-vessels." 



