202 MOLIUSCA. 



cancellated, M. Dactylus; and Conohelix (our fig. 432), to 

 whicli is given the prior name, Imbricaria, Schum. 



MITEELLA. Sw. A genus consisting of Mitea Tissurella, 

 casta, Olivseformis, and similar species, described as " Eather 

 small ; olive-shaped ; unequally fusiform ; always smooth and 

 polished, and sometimes covered with an epidermis ; base obtuse 

 and effuse ; spire nearly or quite equal to the aperture ; plaits of 

 the pillar few, oblique, and extending beyond the aperture, 

 which is smooth internally." Sw. p. 321. M. Fissurata, E. M. 

 371. f. 1. OUvarii, f. 2. Dactylus, 872. f. 5. Ex. Mitra bicolor. 

 PL xxvi. fig. 559. 



MITEEOLA. Sw. A genus of" Mitranse," Sw. thus described : 

 " Small ; unequally fusiform ; the base obtuse ; inner lip, 

 typically thickened, inflected, and either toothed or tuberculated ; 

 plaits on the pillar distinct, the inferior largest ; tip of the spire 

 sometimes papillary ; aperture without either striae or groove." 

 Sw. p. 320, M. Monodonta, M. Trebellum, Zool. Illustr. II. 

 128. f. 1. f. 2. PI. xxvi. fig. 558. 



MODIOLA. Lam. {Modiola, a little measure.) Fam. Myti- 

 lacea. Lam. — Descr. Equivalve oblique, cuneiform, inequilateral, 

 thin, with the anterior side short and narrow, slightly gaping to 

 admit the passage of a byssus, and the posterior side elongated, 

 broad, sub-quadrate ; hinge thin, toothless, rectUiaear, with a 

 long, partly external ligament ; muscular impressions two iu 

 each valve; palleal impression irregular, not sinuated. — Obs. 

 This genus differs from Mytilus, to which the common muscle 

 • belongs, ra the anterior margin being rounded out beyond the 

 umbo, which in Mytilus is terminal. The Lithodomi _may be 

 known from this genus by their cylindrical form. M. Tulipa. 

 PL ix. fig. 160. 



MODIILUS. G-ray, 1840. Species of Monodonta. Lamarck, 

 typified by Trochus modulus. 



MOLLTJSCA. (From Mollis, soft.) The twelfth class of inver- 

 tebrated animals with univalve shells or none ; divided into the 

 following orders : Pteropoda, Gasteropoda, Trachelipoda, Cepha- 

 lopoda, Heteropoda, fig. 220 to 488. The tertn mollusca is also 



