xl 



We find that, while some groups of species extend 

 over a very wide territorial space, other groups are 

 extremely restricted, and yet are frequently charac- 

 terized by as great variation in form, size, orna^ 

 mentation, etc., as the former. The Goniohasic 

 Group occupy the entire extent of our country, 

 represented by the sole species of our Northern 

 Atlantic States, the very few forms of the great 

 Northern Lakes and the species of the Pacific States, 

 while they also occupy the entire southern country, 

 with one or two species in Mexico and Cuba. 



The Trypanostomoid Section, on the contrary, is 

 very much more restricted, being confined princi- 

 pally to the streams tributary to the Mississippi and 

 the Gulf of Mexico. The Mississipj)i appears to 

 form their western boundary. 



While the Trypanostomoid forms attain their 

 maximum development in size and number in the 

 Tennessee River, they are, to a very great extent, 

 replaced by the Goniohasic forms in the Coosa 

 Eiver, which is undoubtedly the metroj)olis of the 

 latter. The most striking genus of each of these 

 groups is absolutely confined to the respective 

 streams in which the groups had their origin. Thus, 

 lo and Sckizostoma are inhabitants, the first of the 

 Tennessee and branches, the second of the Coosa, 

 and neither of them is elsewhere found. 



Assuming the Ohio River as a dividing line, we 

 find that ninety-five per cent, of all the species 

 originate south of it. Even a smaller proportion 

 inhabit the rivers east of the Alleghany, and west 

 of the Rocky Mountains. In the west, no species of 

 StrepomatidcG have been discovered in higher lati- 

 tudes than the northern boundary of the United 

 States, while in the east, the St. Lawrence River 

 and tributaries appear to be the northern limit of 

 the family. 



We thus find the Strepomatida' to be distributed 

 almost exclusively within the limits of the United 



