DEC APOD A. PINNOTHEWDM. 



BRACHYURA. 



GENUS PINNOTHERES, LATR. 



CANCER, Linn. Fabr. Herbst, Penn. 



PINNOTHERES, Latr. Leach, Edwards. 



Generic character. External antennce very short, occupying the 

 inner canthus of the orbit. External pedipalps oblique ; the se- 

 cond articulation rudimentary, the third large, and forming the 

 whole valvular portion ; the fourth inserted at the extremity of 

 the previous one; and the fifth giving attachment to the sixth 

 at the middle of its anterior margin, resembling the thumb of a 

 didactyle hand. Anterior legs equal, the remaining pairs some- 

 what compressed ; the terminal joint acute, curved, and strong. 

 Eyes inserted on very short peduncles, distant. Orbits nearly 

 circular. Carapace nearly circular, rounded at the anterior mar- 

 gin. Front not united to the epistome. Abdomen seven-jointed 

 in both sexes ; that of the male small, of the female extremely 

 broad, round, and prominent. 



THE species of this genus are very remarkable from the 

 peculiarity of their being indebted to animals of a very 

 different class for protection, although not truly parasitic. 

 They are found always to inhabit the shells of the Bivalve 

 Mollusca, principally of the genera Mytilus, Modiolus, and 

 Pinna^ and occasionally also of Ostrea, Cardium, and other 

 genera ; and this habit, which was well known to the 

 ancients, gave rise to some interesting and curious hypo- 

 theses and fables, which will be alluded to hereafter. The 

 males are always very much smaller than the females, and 



