[ 193 3 



21. Experiments might be tried to afcertain 

 whether pearls are not fuch concretions in the 

 fhells wherein they are found, as the crabftones 

 (lapides feu oculi cancrorum) in the fhells of 

 the river cray-fifh, which collect alkaline or cal- 

 careous materials from the food of the animal for 

 the formation of the new fhell, as do the mya and 

 mytihis margaritifer a new layer for the increafe 

 of their fhells. Do the fhells containing the pearls 

 gradually increafe through the year, or at a cer- 

 tain feafon only ? 



22. It mould be carefully remarked which of 

 the fhells, efpecially of the murex and turbo 

 kinds, afford a red or purple juice fit for Rain- 

 ing or dying like the purple of the ancients ; 

 whether the dye be permanent, and the method 

 of preparing and applying it by fome Indian na- 

 tions. D'Ulloa, in his South-American Voyage, 

 Vol. I. page 182, fpeaks of one of thefe fhells 

 found near Panama on the Darien Iflhmus ; and 

 Janus Plancus, or Giovanni Bianchi, in his work 

 on fhells, mentions the turbo fcalaris Linra. or 

 wendeltrap, as affording the violet purple of the 

 Romans. 



23. Defcriptions and drawings of the animals 

 or polypes inhabiting the various corals, coral- 

 lines, fppnges, echini, or fea-eggs, afteriae or 

 ftar fifh, fepiae or cuttle fifli, holothuria^ or fea- 

 nettles, and all the various mollufca, and the po- 

 lypes of the tubipores, madrepores, millepores, 

 cellepores, Sec. deferve the attention of a natural 

 hiftorian, as but few of them are well defcribed 

 or known, 



C c SECT, 



