NUMMULACEA. Bl. The third family of Cellulacea, Bl. described as containing shells or calcareous bodies, which are characterized as discoidal, lenticular; without the slightest traces of whorls to be seen externally. The whorls are numerous, internal, and divided into a great number of cells, which are separated from each other by imperforate septa. This family contains the genera Nummulites, Siderolites, Vorticialis, Helicites, Orbiculina, Placentula. NUMMULTTES. Lam. (_Nummus_, money.) _Fam._ Nautilacea, Lam.--_Descr._ Orbicular, convolute, shewing no trace of spire externally; interior divided into cells spirally arranged.--_Obs._ The singular fossils composing this genus receive their name from their external resemblance to a battered coin. Fig. 472. N. lenticulina. NUX. Humph. CYCLAS, Lam. NYMPHACEA. Lam. A family belonging to the order Conchifera Dimyaria, Lam. Ligament external, placed on a prominent fulcrum. This family contains the following genera: 1. SANGUINOLARIA. Rostrated, gaping; two cardinal teeth in each valve, including _Soletellina_ and _Lobaria_. Fig. 98, 99. 2. PSAMMOBIA. Quadrate; valves closed, including Psammotæa. Fig. 100. 3. CORBIS. Thick, fimbriated; a cardinal tooth in the centre of a pit. Fig. 101. 4. GRATELOUPIA. A series of small teeth filling a triangular area. Fig. 102. 5. EGERIA. One single and one double cardinal tooth. Fig. 103. 6. LUCINA. Rounded; anterior muscular impression tongue-shaped. Fig. 104. 7. TELLINA. An anterior fold in the ventral margin; lateral teeth. Fig. 105, 106. 8. TELLINIDES. No anterior fold; no lateral teeth. Fig. 107. 9. DONAX. Margin denticulated; shell wedge-shaped. Fig. 108. 10. CAPSA. Margin not denticulated, no lateral teeth. Fig. 109. OBELISCUS. Humph. TROCHUS, Lam. OBLIQUE. (_obliquus._ lat.) In a slanting direction. The whorls of spiral univalves generally take an oblique direction in reference to the imaginary axis of the shell. A bivalve is said to be oblique when it slants off from the umbones. An example of this is seen in Avicula, fig. 163. OBSOLETE. (_obsoletus_, lat.) Worn out, out of use. This term is used to express an indistinctness of character, which sometimes results from the action of sea-water upon unprotected parts of the shell, and sometimes from the deposits of enamel formed in age, and covering the early striæ, ribs, teeth, &c. thereby rendering them less acute. OBTUSE. (_obtusus_, blunt.) The application of this term is not peculiar to conchology. It is most frequently used to express the character of the spire. _Ex_. The apex of Megaspira, fig. 294. OCEANUS. Montf. ("Corne d'ammon vivant," Fr.) NAUTILUS umbilicatus, Auct. OCTHOSIA. Ranz. CLITIA, Leach.