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of water to and from the branchiae. They include the gigantic Pinna of 

 the Mediterranean, and more than fifty others of more exotic range, most 

 of them elaborately scaled and some brilliantly coloured ; the beautiful as- 

 semblage of winch the edible and tulip Mussels are the types ; and a group 

 of borers which, notwithstanding their confined habits, have shells with a 

 most delicately sculptured and silken surface. With a few very limited ex- 

 ceptions, they are inhabitants of the sea. The genera are — 



Pinna. Mytilus. Modiola. Lithodomus. 



Genus 1. PINNA,.Z««»##s. 



Animal ; triangular ; mantle freely open ; no siphons ; mantle 

 margins with serrated edges ; month with foliaceous lips and 

 short palps ; arms furnished with a long ligulate valve ; foot 

 small, with a byssal groove ; adductor muscles very unequal. 

 (Forbes.) 



Shell; equivalve, oblique, longitudinally wedge-shaped, fibro-lami- 

 nar, generally scaled ; hinge lateral, toothless, with the ligament 

 rather internal, continued throughout its whole length. 



Authors are somewhat divided as to whether the genus Pinna should 

 be included in this or in the preceding family. Like the Aviculacea, the 

 animal has its mantle-lobes disunited, and there are no siphons ; but in 

 the structure of its shell and in habitat, it partakes more of the character 

 of the true Mussels, in which the lobes of the mantle begin to be united 

 and to form siphons in front. The single species inhabiting our own south- 

 western shores, P. pectinata, is the largest of British mollusks ; and the 

 P. rotundata, inhabiting the Mediterranean, is the largest of the genus. 

 The name given to this shell by Aristotle has survived to this day. Lin- 

 nreus adopted it to designate the genus, and no attempt to divide so na- 

 tural a group into further genera has found favour. 



Among the foreign species, four-fifths of which are inhabitants of the 

 Old World, and one-fifth only of the New, there are most interesting 

 varieties of sculpture. In P. serrata the scales are minute, copious, and 

 sharp ; in P. alia and Cumivgii they are curiously tubular and erectly re- 

 curved : in P. nobilis and rugosa they are promiscuously distorted ; while 

 in many species, as in P.fumata, bicolor, and Philippinensis, the shell is 

 smooth. In examining the Pinna it is, however, important to observe the 

 species in different stages of growth and from different habitats. Indivi- 

 duals which in a young state are characterized by a profusion of scales, 

 often become roughly laminated and even denuded of sculpture; and the 



