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LETTER XIII. 
ALCYONITES AGREEING IN THEIR FORMS] BUT DIFFERING IN 
THEIR STRUCTUllE SPECIMENS OF FROM FRANCE, ITALY, 
SWITZERLAND, AND ENGLAND WILTSHIRE ALCYONITE. 
T HE fossil alcyonium, which I next present to your notice, is considered 
as very rare, both by Mons. D^Annone and Mr. Walch, It is figured 
in Knorrs elegant work. Tome II. Planche, F. 3, from a specimen 
obtained, as were those in my possession, from Randenberg. This 
fossil is figured Plate XL Fig. 2, where it will be seen approaching to a 
hemispheric form : its lower part, where was its pedicle, being somewhat 
conical, and its superior part, which is somewhat rounded, having a 
considerable cavity in its centre. The substance of the fossil is divided 
into numerous lamellas of considerable thickness, perpendicularly disposed 
round this centre, and concentrated at the conical projection in the 
inferior part. Between these lamellcC are grooves of about a quarter 
of an inch in depth, which are transversely divided by grooves less deep, 
and much more irregularly disposed. 
Anxious to obtain some information respecting the structure of this 
strangely formed mass, I devoted one of the curious specimens which 
I possessed to suffer the required examination. By means of attrition 
on a sand-stone of considerable hardness, a polished section was 
obtained on its superior part. On examining this carefully with a 
lens of considerable power, the substance of the alcyonium appeared 
to have been formed in this part of minute tubes, opening side by side, 
in lines crossing each other at right angles. To illustrate this arrange- 
