MYTILUS. 197 



lineata, lb. f. 5. melongena. En. Meth. 435. f. 3. nodosa. Chem. 

 1564. 5." Sw.p. 307. Ex. P. Melongena, Fig. 



MYRTEA. Turt. Venus spinifera, Auct. Lucina spinifera, Non- 

 null. The shells of this genus are described as f« Oval, triangular, 

 equivalve, nearly equilateral, closed. Hinge of one valve with 

 a single tooth, and lateral one on each side ; of the other valve 

 with two teeth, the lateral ones obscure. Ligament external." 

 British Channel and Mediterranean. 



MYSCA. Turt. A genus composed of species of Unio, Auct. 

 which are distinguished by having "strong, transverse, notched, 

 cardinal and long lateral teeth." Unio pictorum. 



MYSIA. Leach. A genus composed of Tellina rotundata, mon- 

 tagu and other similar species. 



MYTILACEA. Bl. The fourth family of Lamellibranchiata, Bl. 

 The shells are described as regular, equivalve, frequently with a 

 thick, horny epidermis. A toothless hinge and a linear ligament. 

 This family contains the genera Mytilus and Pinna. 



MYTILACEA. Lam. A family belonging to the first section of 

 Conchifera Monomyaria, Lam. described as having the ligament 

 partly interior, occupying the greater part of the hinge line, 

 which is straight. The shell is rarely foliaceous. The Mytilacese 

 cannot easily be confounded with the Malleacese, because the 

 former are generally regular and the latter are irregular, and have 

 a thick internal coating of pearl, beyond which the external 

 coating extends. The genera may be thus distinguished ; 



1. Mytilus. Umbones terminating in a point. Fig. 158. 



2. Dreissina. The same, with a septiform plate. Fig. 159. 



3. Modiola. Anterior margin rounded beyond the umbones. 



Fig. 160. 



4. Pinna. Open at the posterior extremity. Fig. 162. 



5. Lithodomus. Cylindrical, living in holes. Fig. 161. 

 MYTILUS. Auct. Fam. Mytilacea. Lam. — Descr. Equivalve, 



cuneiform, oblique, smooth, with umbones terminal, pointed, and 

 posterior side broad, rounded ; hinge linear, with a long, partly 

 internal ligament ; muscular impressions two in each valve, that 



