vr Neri vs. 
VOL. Vu. OCTOBER, 1898. No. 6 
ILLUSTRATIONS OF MEXICAN MELANIANS.! 
BY H. A. PILSBRY. 
The distribution of the Melanians and of land operculates in the 
Americas forms a most interesting chapter in zoogeography. As is 
well known, the family Plewroceride comprises all of the Melanians 
found living in North America above the Rio Grande; and more- 
over no members of this family or subfamily are known to exist out- 
side of this area. South of the Texas boundary there are few mela- 
nians or none throughout northern Mexico; but as we approach the 
isthmus of Tehauntepec the characteristic neotropical genera Pachy- 
chilus and Hemisinus appear, and are represented by a considerable 
number of species and innumerable local races. The richness of 
this fauna in varietal forms rivals the prolific streams of Tennessee 
and northern Alabama. Every spring and stream has its peculiar 
variations, often so distinct typically, that the naturalist is tempted 
into extravagance in naming them as species. The illustrations here 
with given represent some of the forms of Pachychilus glaphyrus 
from the State of Tabasco, sent to the Academy of Sciences by 
Professor Rovirosa, a zealous and enlightened naturalist of that 
State. 
v Reprinted by permission from the Proc. Acad. Nat. Sci., Phila. 
