on Shell and Bone. 27 



«haraAcrs, be enabled to afcertain the clafs to which the 

 echinus was to be referred. 



Of the three echini wliich were examined, one' had fmall 

 fpines; the fecond had large obtufe fpires; and the third 

 was of a very flat form. 



Portions of thefe echini were feparatcly immerfed in acetous, 

 muriatic, and diluted nitric acid, by each of which they were 

 completely diflblved with muq^ effervefcence; depofiting at 

 the fame time a thin outer (kin, or epidermis. The tranfpa- 

 rcncy of the folutions was alio difturbed by a portion of gluten 

 which remained fufpended, and communicated a brown: fli 

 colour to the liquors. 



The i'olutions in acetous and diluted nitric acid were fil- 

 trated ; after which, from the acetous folution of each echi- 

 nus, I obtained a precipitate of phofphate of lead by the ad- 

 dition of acetite of lead ; and having thus proved the pretence 

 of phofphoric acid, I faturatcd the nitric folutions with pure 

 ammoniac, by which a quantity of phofphate of lime was 

 obtained, much inferior, however, in quantity to the carbo- 

 nate of lime, which was afterwards precipitated by carbonate 

 of ammoniac. 



The compolition of the cruft of the echinus is therefore 

 different from that of marine fhells ; and by the relative pro- 

 p^jrtions and nature of the ingredients, it approaches moft 

 nearly to the fliells of the eggs of birds ; which in like man- 

 ner confili of carbonate, with a hnall proportion of phofphate 

 of lime cemented bv gluten. 



It remained now to examine the compofition of thofe fub- 

 fiances which are decidedly called cruftaceous ; but previous 

 to this, fome experiments were made on the afterias or Itar- 

 fifli, of which 1 took the fpecies commonly found on our 

 eoalls, and known by the popular nanie of five fingers {ajh-- 

 rtns rubeiis.) 



The afierias is thus defcribcd by Linnaeus. *' Corpus de- 

 '* preflUm, fubtus fulcatumj crulta coriaeea, tentaculis mu- 

 ricata.*." 



When the afterias was immerfed in the acids, a confidcr- 

 ablc effervcfcence was produced, and a thin er.ternal itratum 

 * tj)ftema 'Naturae. Ed. Gmclin, p. 3160. 



E 3 \va.^ 



