188 MYTILID^. 



Modiolus, from which, however, its brilliant colouring will 

 almost always distinguish it. The 31. Australis of Gray- 

 is much more closely allied to it, and indeed is barely 

 distinguishable in certain of its forms. 



Typically this is a thin and elongated species, and is 

 rather more produced when adult than are individuals of 

 Modiolus of similar dimensions ; to that species indeed its 

 general outline and characters wear so close a similitude, as 

 to render unnecessary any detailed account of its propor- 

 tions. It is rather more cylindrical, being somewhat more 

 swollen at the diagonal elevation, is usually less broad at 

 the hinder termination, and has the upper posterior outline 

 occasionally, but obscurely, subretuse ; the anterior side, 

 although very short, is nevertheless rather more prominent 

 likewise. The epidermidal coating is, in our British spe- 

 cimens, of a fulvous cast on the adult, and bright yellow in 

 the immature examples, and being transparent, exhibits the 

 exquisite crimson painting which ornaments the posterior 

 surface of the valves. This painting consists of narrow and 

 generally numerous linear rays, either simple or more 

 usually composed of linear angulations ; occasionally the 

 entire posterior triangle is wholly or partially clouded with 

 these minute and radiatingly disposed zigzag lines. We 

 have not perceived any distinct beard on any of the indi- 

 viduals we have examined. The beaks are sometimes 

 stained with crimson. The internal nacre, which has often 

 a pale bluish cast, generally, if not always, displays the 

 external radiation. Our largest typical specimen only 

 measures an inch and a half in length, and three-quarters 

 of an inch in breadth. Dr. Philippi, whose Sicilian ex- 

 amples are identical with those we have ourselves taken, 

 but have their epidermis of a brownish horn-colour, mentions 

 a variety with violet rays, and another with only obsolete 



