NATICA effusa.
N. testâ depressâ, albâ, maculis castaneis ornatâ; spirâ brevissimâ; columellæ basi crassâ, planâ, ad labium interius sinu annexâ.
Shell depressed, white, with chesnut spots; spire very small; umbilicus large, open, spreading; base of the pillar thick, flat, and united to the inner lip by a sinus.
In form, and sometimes in colour, this shell bears a close resemblance to the oval variety of N. mamilla (Nerita mamilla Lin.); but, the umbilicus, instead of being entirely closed up, is remarkably open, very deep, and the pillar forming an elevated ridge within; colour in the shells of this genus is a very secondary, and, in many cases, a most fallacious guide for the discrimination of the species; for this is sometimes pure white, and I have specimens of N. mamilla entirely orange. This is a rare shell, probably from India.
