50 
TRANSACTIONS OE THE TEXAS ACADEMY OE SCIENCE. 
are, as a rule, hardly felt here in the interior. On the coast they are 
usually light, and occur normally only in January and February. 
A coccid secured at Laguna, which comes within this fauna, proves to 
he extremely closely allied to the notorious Diaspis amygdali of the West 
Indies, Australia, etc. 
ISTHMUS OF TEHUANTEPEC (southern Vera Cruz and Oaxaca). 
During the last two weeks of May, a trip was made by rail from Coatzo- 
coalcos across the Isthmus of Tehuantepec to Tehuantepec City, and 
Salina Cruz on the Pacific coast; returning horseback later from Salina 
Cruz to Tehuantepec. 
The Atlantic (Gulf of Mexico) slope of the Isthmus of Tehuantepec 
is Tropical, hut on the Pacific slope a change is noticeable. The soil 
and vegetation are more arid in character, and pertain to the Lower So- 
noran. Around Tehuantepec City, for instance, the aspects of the coun- 
try and vegetation are those of Sonora, or southern Arizona. On the 
railroad, long before reaching Tehuantepec City, while going down 
amongst the hills, the tall cacti and other plants indicate distinctly the 
Lower Sonoran . This shows the Lower Sonoran zone to run far on south 
of the latitude of Oaxaca city, as mentioned in my previous paper, along 
the Pacific slope of the Isthmus, and douhtess continuing down through 
Chiapas. Moreover, the Lower Sonoran extends down in places over the 
whole Pacific slope of Mexico to the seacoast itself, judging from the 
conditions on the Isthmus of Tehuantepec and in southern Sonora, 
and is not bordered by a continuous tropical coast strip, as on the Gulf 
of Mexico coast. The Tropical exists here along the Pacific slope only 
in broken patches, in river and mountain valleys and favored spots, like 
deep barrancas, where the soil and the rainfall are adapted to it. The much 
greater absence of rainfall on the Pacific slope is the cause of this rather 
remarkable variance in biogeographic conditions. Sumichrast has re- 
marked (Bull. U. S. Nat. Mus. No. 4) on the differences in the bird 
faunas of the Atlantic and Pacific slopes of the Isthmus of Tehuantepec. 
Of course, it must he remarked that the economic possibilities of the 
flora here are Tropical , provided irrigation and artificial soiling are re- 
sorted to where needed, hut the natural or meteorologic conditions con- 
trol the native fauna and flora, and preserve those characteristic of an 
arid or suharid region, except in the case of the more favored Tropical 
patches and valleys. 
Some scale-insects of much interest were secured in the Lower Sono- 
ran between Tehuantepec City and the coast. The immense monoph- 
loehid, Llaveia axinus , was rediscovered. A new species of Lecaniodias- 
pis ( Prosopophora ) was found, being the first finding of the genus in 
Mexico. Ceroplastes mexicanus, originally discovered by the writer at 
