MULTIVALTE. 205 



our plates- The reason why this substance is called mother-of- 

 pearl is that the true pearls are produced from its surface. 

 They arise principally from accident or disease, and are some- 

 times artificially produced by pricking through the outside of 

 the shell while the animal is living. The animal is allowed to 

 live until it has formed a pearl over the wounded part. 

 MOTJLIlSrSIA. Grrateloup. Pupina, Vignard. A genus of small 

 land shells with enamelled surface and spiral operculum. See 



PtTPrtTA. 



MOTJEETIA. Gray. " Gadin," Admson. A genus of patelli- 

 form shells, described as differing from Siphonaeia (the original 

 Mouretia of Adanson) in the situation of the siphon, which in 

 Mouretia is close to the place where the muscular impression 

 is interrupted to leave a space for the head ; while in Siphonaria 

 it is nearly half way between the anterior and posterior ends of 

 the shell. 



MOUTH. The aperture or opening of univalve shells. 



MULIIS'IA. Gray. A genus composed of species of Mactea, 

 Auct. described as having the ligament (properly so called) in- 

 ternal, and lateral teeth simple. M. bicolor ; Mactra, Auct. 

 PL iv. fig. 82. 



MTJLLERIA. Per. Fam. Ostraeea. Lam. — Bescr. Irregular, sub- 

 quadrate, inequivalve, inequilateral, foliaceous, attached, pearly 

 within, green, horny without; hinge irregular, with a partly 

 external ligament, passing to the interior, through a sort of sinus. 

 — Obs. This remarkable shell resembles Etheria in general form 

 and appearance, but is distinguished by having only one muscu- 

 lar impression. It is so rare that, although not very beautiful, 

 a specimen has been known to produce £20. at a sale. PL xi, 

 fig. 192. 



MYLTILOCrLAE. Many chambered. 



MULTISPIEAL. {Multus, many ; spira, spire.) A term applied 

 to a shell when the spire consists of numerous whorls ; or to an 

 operculum of numerous volutions. 



MTJLTIVALYE. {Multus, many ; valva, valve.) Consisting of 

 numerous valves. There are three kinds of multivalve shells : 



