MACTRACEA. 181 



MACROSPIRA. Guild. A genus composed of Helix octona, 

 Auct. Macrospira aperta, Guild. 



MACROSTOMATA. Lam. (Ma/cpoe, macros, long ; arofxa, stoma, 

 mouth.) A family belonging to the first section of the order 

 Trachelipoda, the shells belonging to which are described as 

 haliotoid or ear shaped, with a very large aperture, destitute of 

 an operculum. This family contains the following genera, which 

 maybe thus distinguished. 



1. Velutina. Globose, with velvety epidermis. Fig. 337. 



2. Stomatia. Ear-shaped ; pearly within ; including Sto- 



matella. Fig. 335, 336. 



3. Sigaretus. The same, not pearly ; including Cryptostoma. 

 Fig. 334. 



4. Coriocella. The same, thin, transparent. 



5. Haliotis. The same, not thin, nor transparent ; with 



holes ; including Padollus. Fig. 338, 339. 



6. Scissurella. Heliciform, with a slit near the aperture. 

 Fig. 340. 



7. Pletjrotomaria. Trochiform, with a slit at the edge of 

 the aperture. Fig. 341. 



MACTRA. Auct. (Mactra, a kneading trough.) Fam. Mac- 

 tracea, Lam. Conchacea, Bl. — Descr. Usually thin, equivalve, 

 sub-equilateral, sub-trigonal, slightly gaping at the extremities ; 

 hinge with one cardinal tooth, divided into two parts, diverging 

 from the umbo, with sometimes a very small laminar tooth close 

 to its side ; a deep triangular pit near the centre, containing the 

 cartilage ; one long, lateral tooth on each side of the umbo in 

 one valve, received between two in the other ; muscular impres- 

 sions two, lateral ; palleal impression with a small sinus. — Obs. 

 This genus contains many species of beautiful shells found in 

 various parts of the world, some are common in Britain. Fossil 

 species are not numerous, they occur in the tertiary strata. 

 Fig. 79 to 82. 



MACTRACEA. Lam. A family of the order Conchifera Dim yaria, 

 Lam. Sect. Tenuipedes. The cartilage placed in a trigonal 



