^P. duplicata.^ This is even more abundant than /P. heros/. It has a flatter shell, with an obtuse apex and dome-like spire. The umbilicus is partly or wholly closed by a thick, callous, shelly process thrown off from the columellar lip, and is chestnut in color. The surface of the shell is smooth, often polished, ashy-white below and light chestnut above. The operculum is corneous. The length of the shell varies in different localities from one half of an inch to about two [pg368] inches; the breadth slightly exceeds the length. /P. duplicata/ has a very extensive range, from the Gulf of Mexico to Newfoundland. The largest and finest specimens are found in the vicinity of New York and at Hatteras. In Florida they are usually smaller. This species cannot be confounded with any other upon our coast on account of the heavy callous deposit over the umbilicus. Its habits are similar to those of /P. heros/. [Illustration: /Polynices duplicata./] [Illustration: /Natica clausa./] ^Natica clausa.^ A Northern species which is fairly abundant on the Maine coast. It has a shelly operculum, and the umbilicus is neatly closed by a pure white, shining callosity. Its length is about one half an inch, its color livid white to light brown, white within. The calcareous operculum at once determines this shell. This species (as well as the following one) has retained the generic name of /Natica/ because of the shelly operculum, as explained below. ^N. canrena.^ One of the handsomer species of /Natica/, which occurs in Florida. Sometimes it is seen as far north as Hatteras. The shell is white, with bars of light chestnut circling the whorls, and with zigzag lines of darker purplish hue crossing them. The base of the shell is white. The aperture is large and flaring, and is purplish within. The umbilicus is partially closed by an entering callous plug. The operculum is calcareous, with eccentric, deeply cut grooves. Found in sandy stations just about low-water mark. (Plate LXVIII.) ^P. lewisii.^ A species which occurs on the west coast of the United States. It resembles its New England relative /P. heros/ very closely. /P. lewisii/ is a Northern species, and does not range south of Oregon. Professor Keep mentions one specimen of the size of a six-inch globe, but such dimensions are very unusual. A good-sized specimen need not exceed four inches in height. ^P. recluziana.^ A species well known on the southern coast of California. The umbilicus is closed by a thick, highly polished white callosity, and the general shape of the shell is strongly suggestive of the common east-coast species /P. duplicata/. A large specimen is about two inches in diameter.