Generic Type _Nerita Glaucina_ Pennant, &c.
_N. testâ sub-globosâ, fuscâ, albo fulvoque fasciatâ, juxta suturam striatâ; labio exteriore suprà leviter emarginato; umbilico magno, aperto; columellâ obsoletè terminante._
Shell sub-globose, striated near the suture, brown, banded with white and fulvous; outer lip above slightly emarginate; umbilicus large, open; pillar termination nearly obsolete.
_Martini_ 5. _pl._ 187. _fig._ 1872 _&_ 3. _fig._ 1874 & 5? _pl._ 188. _fig._ 1896, 8 _&_ 9.
_Seba_, _pl._ 38. _fig._ 66. _pl._ 41. _fig._ 14, 15.
The Shells of this genus are composed of such of the Linnæan _Nerits_ as are umbilicated, from which latter they essentially differ, both in the organization of the animal and the construction of the shell, which is either closed by a shelly or horny operculum.
The species are numerous, and are found both in temperate and tropical seas; two or three inhabit our own coasts, but by far the greater number are found in the Asiatic Ocean. They are subject to variation in their colour; and this, joined with a general resemblance in form, has rendered the discrimination of the species very difficult. I have, however, remarked, that the various modifications of the umbilicus, and the termination of the pillar (which is indicated in many species by an elevated ridge or rib within the umbilicus) is a certain and constant indication, presenting the same peculiarity through all the individuals of a species, even in the young state. This termination of the pillar has been mistaken for the inner lip, which, on the contrary, is always above the umbilicus, which, if closed, is not closed by the lip, but by the thickened termination of the pillar or columella.
The two most striking varieties are here figured of this species, which is sufficiently described in the specific character. I believe it is found both in the Mediterranean and Red Seas.
_M. viridis, subtus albescens, uropygio caudâque cæruleis; vertice, strigâ oculari, fasciâque latâ collari nigris; mento, superciliisque albis; rectricibus mediis elongatis._
Green; beneath whitish; rump and tail blue; crown of the head, eye stripe, and broad band across the neck, black; chin and eye-brows white; two middle tail feathers lengthened.