"Get four bit for tia Marta!"

In California "four bits" means a half dollar. Occasionally somebody
on the overland train that stopped at the station in town would be
attracted toward a spiny "horned toad" as a curiosity, and would buy
one. Arturo meant to try to sell this specimen in that way. If he
got the money, he would give it to tia Marta.

Tia Mama was Arturo's aunt. "Tia" means "aunt" in Spanish.
Presumably for the reason that nephews are sometimes troublesome to
their aunts, there is a Spanish proverb that warns a nephew against
making his aunt too frequent visits:

En casa de tia, Mas no cads dia:' ("In the house of thy aunt, But
not every day.") Notwithstanding this adage, however, the boy Arturo
lived with his Aunt Marta. This was not always pleasant, for neither
Arturo nor tia Marta was perfect. Yet they really thought a good
deal of each other. The third member of the household was Tia
Marta's husband, do (uncle) Diego, but he was very old and lame, and
could not work. Tia Marta earned the living, and Arturo usually
thought of himself as dwelling with tia Marta rather than do Diego.
Arturo never quarreled with his uncle.

When the overland train stopped at the station for water, and Arturo
rushed breathlessly to sell his horned toad, the eager boy found no
passenger who was desirous of being a customer save an old gentleman
who doubtfully offered twenty-five cents for the creature. 'Arturo
stuck bravely to his intended price of "four bits," but the train
creaked for starting, and, alarmed, the boy hastily handed over the
toad, took the quarter of a dollar, and rushed off the train.