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XI. A Dijfertation on thofe fojftl fgured 
Stones called Belemnites ; communicated in 
a Letter from Mr. Emanuel Mendez da 
Cofta to Martin Folkes, Efq ; Pr . R . S \ 
SIR, 
Read]™. ^•’TT^HE Origin and Nature of the Be - 
* 746 ' 7 ' J. lemnttes having lately been greatly 
controverted, I have taken the Liberty ro add re ft to 
you the following Thoughts on that Subject $ and 
beg, Sir, if you think them worthy your Regard, you 
would lay them before' the Royal Society , as a due 
Teftimony of the great Refped 1 have for that 
Learned and Iiluftrious Body. 
The Belemnites.'is a Foflil of different Magnitudes 
and Colours, ever regular in Shape, which is either 
cyimdric, conic, or thereunto approaching. Numbers 
of them have, on one Side only, a Chap or Seam run- 
ning their whole Length 3 others have it in Part $ and in 
others it is not at all to be obferved : it confifts of a 
talcy Matter, with an Intermixture of Spar or Cryftal, 
dhpofed in Stria from or near its Centre to its Cir- 
cumference, and is made up of Crufts inclofing each 
other, the inner-mod whereof is as regular as the 
ourermoft. Sometimes, tho* feldom, in comparifon 
to the Numbers of the Belemmtes , in the Centre is a 
Cavity ever conic, whatever the external Shape of 
the Belemnites be. This conic Cavity is at different 
tunes empty, or elfe filled, either with a tolid Body 
of mineral Matter,. Cryilal, Stone, Byrites , &c. or 
with 
