The ridges of the snail shell spiral to the left which is an example of sinistrorsa.
Sinistro is defined as toward the left.
An example of sinistro is sinistrorse, which means twining upward toward the left.
of, at, or toward the left: sinistrodextral
also, before a vowel, sin′istr-
Origin of sinistro-from Classical Latin sinister: see sinister