HEMICYCLOSTOMATA. Bl. The fourth family of Asiphonibranchiata, Bl. described as "more or less globular, thick, flattened on the under side; spire very short; aperture large, semilunar, entire; its outer edge hollowed; its inner or columellar edge straight, sharp and septiform." This family answers to the genus _Nerita_ of Linnæus, and to the family Neritacea of Lamarck. It contains the genera Natica, Nerita, Neritina, and Navicella. HEMIMACTRA. Sw. A sub-genus of Mactra, thus described: "General form of _Mactra_; but the cardinal teeth entirely wanting; cartilage internal, central, in a large triangular cavity; lateral teeth 2/1, distinct, lateral, striated: connected to the _Glycimeri_. H. gigantea, _Lam._ v. 472. No. 1. grandis, _Sw._ Sp. Nov." Sw. p. 369. HEMIMITRA. Sw. A sub-genus of Paludomus, Sw. (Melanianæ.) HEMIODON. Sw. A sub-genus of Anodon, described as having "Tubercles or undulations on the hinge margin. H. undulatus, purpurascens and areolata." HEMISINUS. Sw. A sub-genus of Melania, thus described: "General shape of _Melania_; but the base of the aperture is contracted and emarginate; outer lip crenated. H. lineolata, Griff. Cuv. xii. pl. 13. fig. 4." HEMITOMA. Sw. A sub-genus of Emarginula, thus described: "Patelliform; the fissure not cut through the shell, but merely forming an internal groove. H. tricostata, _Sw._ Sow. Gen. fig. 6." HEMITROCHUS. Sw. A sub-genus of Geotrochus, Sw. H. hæmastoma. Sw. p. 331. HEPTALASMIS. Leach. ([Greek: Hêpta], _hepta_, seven; [Greek: elasma], _elasma_, plate) A small shell resembling Pentelasmis, from which it differs in the number of valves, being composed of seven valves according to Leach, and of eight according to Gray, who counts the dorsal valve, which is jointed, as _two_, and names his genus Octolasmis. Fig. 41, H. Warwickii. HERCOLES. Montf. A microscope shell, appearing from De Montfort's figure to resemble TROCHUS _Imperialis_ in shape. HERION. Montf. LENTICULINA, Bl. Microscopic. HERMAPHRODITA. Bl. The third sub-class of Paracephalophora, Bl. divided into, Sect. 1, _symmetrical_, containing the orders Cirrobranchiata and Cervicobranchiata; Sect. 2, _non-symmetrical_, order, Scutibranchiata. HERMES. Montf. A genus composed of CONUS _Nussatella_, Auct. and other elongated, cylindrical, striated species. Fig. 460. HETEROBRANCHIATA. Bl. The fourth order of the class Acephalophora, Bl. containing no testaceous mollusca. HETEROPODA. Lam. The fifth order of the class Mollusca, Lam. This order contains but one genus of shells, viz. Carinaria, fig. 488. HETEROSTEGINA. D'Orb. A genus of microscopic Foraminifera.