INTRODUCTION. XXVil 
var. hiabundus), and Glandina sowerbyana*. Eucalodium, on the contrary, is wanting 
on the Pacific slope of Guatemala.” 
It must be borne in mind, however, that in Costa Rica the environs of San José 
have been more thoroughly explored by various collectors than the more remote lower 
districts ; this will account for the comparatively large number of species of Strepto- 
styla, Hyalinia, Guppya, and Leptinaria on the central tableland. But it is the more 
remarkable that none of the large-sized freshwater shells, which cannot be easily 
overlooked, as Ampullaria, Pachychilus, Unio, and Anodonta, have hitherto been 
found there. 
The differences between the fauna of the Pacific and Atlantic slopes, in both Mexico 
and Central America, are noticed in the Tables: they seem to be not very important 
as regards the land-shells. We find in many instances a very unequal number of 
species, but it must be remembered that in Mexico, Guatemala, Honduras, and 
Nicaragua the Eastern slope is not only broader and provided with larger rivers, 
but has also, at least in Mexico, been more carefully explored by a greater number of 
scientific travellers and residents; it is therefore not a matter of surprise that the 
Eastern slope of these countries has offered, so far, more distinct forms and more 
species to science than the Western, especially among the freshwater shells. In 
* Dr. Stoll possesses a specimen of this species from the Hacienda Buenavista, in the upper part of the 
Cholhuitz district, which has an elevation of 3500 feet (about 1137 m.); this locality was not previously 
mentioned (infra, p. 55), because I had not seen the example. 
+ Fischer and Crosse (Miss. Sci. Mex., Moll. ii. p. 678), speaking of the subregion of the Pacific slope, 
correctly insist on the peculiar geographical range of Holospira—the inland portion of Texas, and from Arizona 
through Coahuila and Chihuahua to the western provinces of Mexico,—corresponding to the range of the 
Cactacean genera Cereus and Echinocereus (also Mammillaria, see K. Schumann, “ Verbreitung der Cactacew,” 
Abhandl. Akad. Berlin, 1899). But they go too far in saying that Holospira is completely absent from the 
Atlantic slope of Mexico: San Carlos, the recorded locality in Chihuahua for H. coahuilensis, var. semisculpta, 
lies very near to the Rio del Norte, and by far the greater part of Chihuahua and of the adjacent State of 
Coahuila are drained by the same river to the Atlantic; moreover, H. teres, var. hoegeana, is found exclusively 
on the eastern slope of the Mexican tableland (see infra, p. 280), H. berendti in the States of Vera Cruz and 
Chiapas (see infra, p. 281), and H. veracruziana near Misantla, also in Vera Cruz (see infra, p. 635). 
+ Fischer and Crosse, in their review of the geographical distribution (Miss. Sci. Mex., Moll. ii. pp. 672, 
678), state that the genus Unio is wanting (“fait défaut”) within Mexico in the streams running to the 
Pacific; but they mention themselves, in the descriptive part (p. 606), that Unio poeyanus, Lea, is found in 
the Rio Balsas, State of Guerrero, which empties into the Pacific. 
