THE HERRING AND ITS ALLIES. 393 



four-fifths of the whole number of factories were included. In 18S0 the 

 number of persons employed in the entire industry was placed at 3,635, 

 the amount of capital invested, $2,362,841, the \alue of i)roducts, $2,116,- 

 787, including 2,066,396 gallons of oil, worth 5733,424, and 68,904 tons 

 of guano, worth $1,301,217. The refuse of the oil factories supplies a 

 material of much value for manures. As a base for nitrogen it enters 

 largely into the composition of most of the manufactured fertilizers. The 

 amount of nitrogen derived from this source in 1875 was estimated to be 

 equivalent to that contained in 60,000,000 pounds of Peruvian guano, the 

 gold value of which would not have been far from $1,920,000. The yield 

 of the menhaden fishery in pounds is probably triple that of any other 

 carried on by the fishermen of the United States. 



In estimating the importance of the Menhaden to the United States, it 

 should be borne in mind that its absence from our waters would probably 

 reduce all our other sea-fisheries to at least one-fourth their present extent. 

 It is therefore of great importance to anglers as well as fishermen. 



In addition to the common Menhaden, a second North American 

 species, Brevoortia patromcs, has recently been discovered. This species 

 has been reported only from the Gulf of Mexico. 



The commercial representatives of the Herring in America are perhaps 

 the River Herrings and the Shad, which ascend our streams in the spring, 

 and, fresh, pickled and smoked, enter very largely into the food resources 

 of the Atlantic region. 



Early writers on American fishes, especially ]\Iitchill and De Kay, seem 

 to have experienced great difficulty in differentiating into species the vari- 

 ous forms of River Herrings or Alewives in our waters. These early 

 writers were, however, apparently more discriminating than some of their 

 successors, for they recognized differences which have been ignored by 

 subsequent writers. They were as much at fault, however, in making too 

 many species, as were Storer and Gill in uniting all the forms under one 

 specific name. 



The attention of the zoologists of the Fish Commission was first called 

 to the probable existence of two species by the persistent opinions of the 

 fishermen of the Potomac, who recognized two forms — differing in habit 

 and in general appearance — which they called the "Branch Herring" 

 and the "Glut Herring" respectively. 



The announcement of the discovery of the two species and a definition 



