Mr. J. S. Miller on Belemnites. 56 



In the Lyas and Lyas-clay, pyrites frequently enters the chambered cone^ 

 which on account of its more fragile construction it is able to attack, whilst 

 the guard resists its operation. Sometimes we meet with the shell of the 

 chambered cone in a semi-decomposed state, involved in pyrites, and flattened 

 as far as it projected beyond the guard, or as far as its latest formed and ad- 

 hering laminiE were unable to resist the pressure of incumbent matter. In 

 other instances we obtain a beautiful conical pyritic cast showing marks of the 

 rim of the concave septa (the outer shell of the cone being destroyed), and 

 the situation of the siphuncle in a series of indentures, which from a hasty 

 and mistaken analogy have been once considered as the spiracula of the Be- 

 lemnite. 



I possess a Belemnite in chert from Dantzic, which is converted into chalce- 

 dony, and where the fibrous structure of the shell is entirely destroyed. The 

 chalcedony has assumed its own mineral figure, and has a mamillated surface in 

 the cavity once occupied by the chambered cone. A transverse fracture shows 

 a few concentric markings common to chalcedonic nodules. 



Miss Benett of Norton House is in possession of a few specimens of Be- 

 lemnites minimus, from near Warminster, (much resembling Parkinson's re- 

 presentation in the 3rd volume of Org. Rem. PI. IV. fig. 14.) which have expe- 

 rienced the changes so often exhibited by the fossils imbedded in green-sand, 

 and which have gradually silicified. It is owing to the kindness of that lady 

 that I have been able to examine these Belemnites carefully. They exhibit in 

 their present state externally a few thin conical lamellae superimposed on each 

 other, and adhering by transverse fibres somewhat analogous to the structure 

 of the common cuttle-fish, and are in many instances hollow in the centre. My 

 explanation of this structure is, that these now siliceous lamellEe have replaced 

 the nacreous layers ; and that the intervening fibrous crystalline substance, 

 as well as the lamellae forming once the centre of the guard, have disap- 

 peared by decomposition. Belemnites of this kind are very rare; and it is 

 interesting that some of these show the same irregular cavities as I noticed 

 in a calcareous specimen in Mr. Greenough's possession, similar to the one 

 figured in Knorr (Vol. iii. Supp, iv. f. fig. 8.). 



Accident furnished another clue to the illustration of the cavities in the spe- 

 cimens referred to, ascribed to the mere dropping out of certain portions of 

 the laminae by decomposition. I observed on the surface of a few specimens of 

 Belemnites from the oolite at Dundry, some circular markings, occasionally 

 one within the other, having an irregular floriform petal-shaped and some- 

 times subvermicular circumference, similar to those represented in Knorr 

 (Vol. 11. part ii. PI, I.* fig. 5.) ; which Walch there considers as marks occa- 



