HIATELLA. Daud. Fam. Lithophagidæ, Lam. A genus composed of species of Saxicava, Auct. which have sharp, angulated, posterior ridges, a circumstance which occurs to many species in a young state, which afterwards become rounded off. Fig. 95, Hiatella biaperta. HIATULA. Sw. A genus proposed to include those species of Oliva, Auct. which have widened apertures. _Ex._ O. Subulata, fig. 458. HIBOLITHES. Montf. A genus composed of species of Belemnites, Auct. which are swelled towards the apex, and contracted near the centre. B. Hastatus, Auct. fig. 468. HIMANTOPODA. Schum. MALLEUS, Auct. HINGE. The edge of the bivalve shells near the umbones, including the teeth and ligament. HINNITES. Defr. A generic name proposed for PECTEN PUSIO, Auct. remarkable for the irregularity of the outer surface, which would almost lead to the belief of its being an attached shell. Fig. 173, H. Pusio. HIPPAGUS. Lea. (_Horse boat._) A minute fossil shell, resembling Isocardia in form, but destitute of hinge teeth. H. Isocardioides, fig. 128. HIPPOCHRENES. Montf. Species of ROSTELLARIA, Auct. with the outer lip spread. Fig. 403. R. Columbaria. HIPPONYX. ([Greek: Hippos], _hippos_, horse; [Greek: onux], _onyx_, nail or hoof.) _Fam._ Rudistes, Lam.--_Descr._ Inequivalve, sub-equilateral, rather irregular, destitute of ligament and hinge teeth; lower valve attached, flat, sub-orbicular, with a muscular impression, composed of two lunulate portions, meeting at one extremity, and presenting the form of a horse-shoe; upper valve conical, with the apex inclined backwards, and the muscular impression marginal.--_Obs._ The earlier naturalists having only met with the upper valve of these shells, placed them among the patelliform univalves; to some of which, particularly Pileopsis, they bear a very strong resemblance. The species of Hipponyx are numerous, and till lately only known in a fossil state. The recent species belong to tropical climates: the fossil species are found in the tertiary beds. Fig. 199, H. Cornucopia. HIPPOPODIUM. Conybeare. _Fam._ Cardiacea, Lam.--_Descr._ Equivalve, obliquely transverse, heavy, deep, inequilateral, umbones incurved; ventral margin sinuated, so as to give a bilobed appearance to the shell; hinge incrassated, with one rugged oblique tooth.--_Obs._ These fossils are found in the upper beds of Lias. Fig. 129, H. Ponderosum.