3 22 Mr. Hatchett’s Experiments 
experiments on three species of the Echinus, with which I had 
been favoured by the Right Honourable President. 
I was the more inclined to begin with the Echini, because 
naturalists do not appear to be perfectly agreed, whether to 
call them testaceous or crustaceous animals. 
Klein, who has written a work upon Echini, after having 
noticed the various opinions of Rondelet, Rumphius, and 
others, determines that they are to be regarded as testaceous 
animals. His words are, “ Sic plurimas testas marinas, in 
“ statu naturali consideratas, cum echinodermatis potius quam 
“ cum crustis astacorum vel cancrorum conferre licebit. Itaque 
“ echinoderma, cum Aristotele, qui echinos inter testacea qui- 
“ bus facultas ingrediendi est reponit, nec non cum Belonio, 
“ Aldrovando, et excellentissimo Sloanio, religiose testam 
“ appellamus, quam satis duram in nonnullis offendimus.” * 
But Linnaeus was of the contrary opinion, as appears from 
his definition of the echinus. “ Corpus subrotundum, cmsta 
“ ossea tectum , spinis mobilibus saepius aspera/’-f 
Now, as the experiments above related had proved, that the 
shells of marine animals were composed of carbonate of lime, 
without any phosphate, I thought it very possible, that the 
covering of the crustaceous animals might, in some respect, be 
different, and if so, I should thus, by chemical characters, be 
enabled to ascertain the class to which the Echinus was to 
be referred. 
Of the three Echini which were examined, one had small 
spines ; the second had large obtuse spires ; and the third was 
of a very flat form. 
* Klein, Naturalis disposilio Ecbinodermatum, &c. p. io. 
f Systema Natures. Edit. Gmelin, p.3168. 
