288 INTKODUCTIOX TO CONCHOLOGY. 



Family lY. Mytilacea. 



It is a pleasant sight 

 To look on creatures formed with wondrous skill ; 

 Perfect in all their parts ; with instincts, too, 

 Of no mean order, by whose promptings they 

 Construct their beauteous homes, or moor their barks 

 To friendly rocks, or range from sea to sea. 



The family Mytilacea have but little affinity with that of 

 Tridacnacea, except in being provided with a fully- developed 

 byssus, consisting of numerous filaments or silky threads, 

 by means of which the mollusk readily attaches himself to 

 rocks or other marine bodies ; and with the assistance of a 

 most curiously-constructed foot he can fix or displace this 

 valuable appendage. 



Shells of the Mytilacea may be described as being rather 

 of an elongate form, regular, equivalve, and generally smooth. 

 Teetli are wanting to the hinge, which consists merely of a 

 strong marginal ligament. The muscular impression is 

 compound, bearing the marks of one or more small acces- 

 sory cartilages, probably destined to assist the muscle in 

 counteracting the strong expanding power of the hinge 

 ligament. 



