184 MARGINAL. 



passing through a sinus in one valve ; hinge rectilinear, length- 

 ened by two auricles ; with a small disc under the umbones, 

 containing the ligament, and a groove containing the cartilage ; 

 muscular impressions one in each valve, large, uniform, and one 

 or two others extremely minute. — Obs. Malleus Vulgaris, the 

 type of this genus, is a most singular shell, commonly called the 

 " Hammer Oyster," from the peculiarity of its shape. It belongs 

 to the Linnsean genus Ostrea, from which it differs in being 

 attached by a byssus. Fig. 165, M. Vulgaris. Tropical. 



MAMILLARIA. Sw. A sub genus of Nattca, corresponding with 

 Polinices of Montfort, having the spire small and the umbilicus 

 filled. Ex. Natica Mamilla, Auct. fig. 327. 



MAMMILLATED. (Mammula, a little teat.) A term applied to 

 the apex of a shell when it is rounded like a teat. Ex. Voluta 

 Vespertilio, fig. 433. 



MARGARITA. Leach. (Margarita, a pearl.) A genus of small 

 shells resembling the genus Trochus, from which it differs in 

 having an operculum consisting of few whorls. M. taeniata, fig. 

 362. Mr. G. B. Sowerby, sen. has enumerated 15 species in a 

 list accompanying the figures published by the author of this 

 manual in Nos. 132 to 134 of his Conchological Illustrations. 



MARGARITACEA. Bl. The third family of Lamellibranchiata, Bl. 

 The shells belonging to it are described as irregular, inequivalve, 

 inequilateral, black or horny without, pearly within ; hinge 

 auriculated, scarcely developed, and without teeth. The ligament 

 is variable and there is a large sub -central muscular impres- 

 sion. This family contains the genera Vulsella, Malleus, Pinna, 

 Crenatula, Inoceramus, Catillus, Pulvinites, Gervillia and Avicula. 



MARGARITACEOUS. {Margarita, a pearl.) Pearly. 



MARGARITANA. Schum. A sub -genus of Uniones, composed 

 of species having " one cardinal tooth," Alasmodon, Say, Mya 

 Margaritifera, Linn. 



MARGARITIFEROUS. (Margarita, pearl ; fero, to bear.) Pearl- 

 bearing. Applied to shells which form pearls ; as Meleagrina 

 Margaritifera, or Pearl- bearing Oyster. 

 MARGINAL. Near the margin or edge. 



