40 LINNEAN GENERA. 



Genus 17— PINNA. 



Animal a Limax ; shell sub-bivalve, fragil, upright, gaping 

 at one end, and furnished with a silky byssus or beard : hinge 

 without teeth. 



Pinna pectinata. — The Pectinated Pinna. Plate VII. 

 fig. 17. Thin, pellucid, light horn coloured ; longitudinally rib- 

 bed^ and spinous for half its width, obliquely striated, transversely 

 on the other half. Six and a-half inches long and three broad. 

 Inhabits the British seas. 



The Pinnae, which frequently grow to a large size, only inhabit the ocean. 

 They are generally found standing erect in the smoother water bays, with 

 the broad end or base of the shell uppermost. They are sometimes affixed 

 by their byssus or beard, to rocks or other bodies, and so firmly attached, 

 that they can by no means be disengaged but at the will of the animal. 



In Italy the byssus of the Pinna is woven into a sort of silk. The fibres 

 or filaments of which it is composed, are very tough, and of a fine glossy 

 brown colour. The ancient Romans highly esteemed articles made of this 

 byssus ; and at Naples and Palermo there are still manufactories of it. Stock- 

 ings, gloves, and even a fabric resembling sarsnet are made from it ; and 

 also an imitation of broad cloths. This latter stufif is very expensive, a coat 

 being about the value of ten pounds of English money. 



The pinna has obtained among the Italians a little reputation for the prac- 

 tice of some of the moral virtues, in treating a small species of crab with 

 hospitality and friendship, by receiving it into the shell, and defending it 

 against its enemies. In return for this kindness, the crab, like the jackal 

 with the lion, acts the part of a provider and monitor, by warning its host 

 of the presence of its prey, or the approach of an enemy. But this friendly 

 intercourse, like the fabulous account of the lion and jackal, accords ill with 

 the nature of the animals between whom it is practised. The crab, it is far 

 more probable, is a troublesome intruder j and, notwithstanding all the 

 service he can repay, is considered a very unwelcome guest, and is indebted 

 for his lodging to his activity and instinctive sagacity in providing for his 

 own personal safety ; retaining possession from the sluggish nature of his 

 host, rather than to his kindness and hospitality. 



Genus 18.— A RGONAUTA. 



Animal a Sepia or Clio ; shell univalve, spiral^ involute, 

 membranaceous, and unilocular, or consisting of a single apart- 

 ment or cell. 



Argonauta Argus. — The Argus Argonauta. Plate VII. 



fig. 18. Involute, extremely fragile, white, ribbed, and obsoletely 



striated; the keels approximate and tuberculated, from six to 



eight inches in diameter ; inhabits the Mediterranean. 



The Argonauta argus, or Paper Nautilus, is the Nautilus so famous 



