7. TROCHUS, _&c._--Some of the species of _Trochus_ surpass even _Emarginula_ in the beauty of their lingual apparatus. The renal organ opens into the bottom of the branchial cavity, contrary to its disposition in _Helix_ and _Lymnæus_, where its exit is near the respiratory orifice. In _Planorbis_, that part of the respiratory cavity receiving the excretions seems separated by an imperfect valve from the right portion. With respect to the secretion of this organ, it consists, in both Gasteropoda and Lamellibranchiata, of numerous pellucid globular bodies, containing opaque earthy nuclei or granules, and presenting different appearances in _Anodon_ (for instance), _Cyclostoma_, _Buccinum_, and _Helix_. When these bodies are incinerated, lime is left, which in some cases appears to have been combined with oxalic acid. The little _Nerita litoralis_ presents the structure of the Turbonidæ very prettily and in small compass, particularly in the very long spiral tongue. _Delphinula_ has the fringed mantle and sides and very wonderfully armed tongue of the other Trochidæ. _Melania_ is of similar organization to our well-known _Paludina_, the stomach compound, the mantle and bilobed head fringed, and the latter marbled like that of _Paludina_. _Ampullaria_ appears to be truly amphibious. 8. BUCCINUM, _&c._--_Natica_ presents much the same structure as the common _Buccinum_, but has a muscular disk anterior to the mouth,--a disposition, with some variations however, found in other mollusks. The first and second stomachs are at a distance from each other, the tongue is little developed, and the branchiæ (often single in the Turbonidæ) two in number. _Purpura_ also differs but little from _Buccinum_. _Ovula_ is a less attainable mollusk: the foot is long and rather narrow, and subventral rather than subtrachelian, with a sinuosity on the right of the neck, where also is a short hooked penis in the male, receiving a vas deferens from near the rectum behind; there is a large and small branchia, and the reflected portion of the mantle is covered with tubercles and tentacles,--no doubt a fine garnish in the living animal; the mouth has a muzzle, and there are small eyes on the external sides of the curved, awl-shaped tentacles; the elements of the tongue are beautifully toothed and serrated.