Organic and Inorganic Changes of Fsivkevia.. 49 



ence that the latter was an intruder either before or after 

 death, that is, while the Parheria was still fresh or unfos- 

 silized. 



We have now to turn our attention for a few minutes to 

 an 2'norganic or mineralogical change which may take place 

 in Parheria ; and for this purpose it is necessary to premise its 

 natural state, so far as ray specimens will allow. 



In the ijurest form, then, that I possess the tubular struc- 

 ture or coenenchyma (coenosteum of Nicholson) is so thin and 

 delicate in appearance and the ultimate structure of its walls 

 so minute that all that I can see in them, under a very high 

 power by reflected light, is an amorphous, pulverulent, trans- 

 lucent substance which, it is worthy of remark, closely re- 

 sembles that of the " shell-fragment " upon which the Par- 

 heria had grown ; and thus I am led to infer, with Prof. 

 Nicholson [op. cit. p. 5), that both originally were of the same 

 nature, that is " calcareous." 



On the other hand, in a less pure condition the lamina or 

 wall thus composed may be more or less covered on each side 

 by a layer of crystalline granular calcite, when, of course, the 

 tubular structure having become thickened becomes more 

 evident, and in this way the greater part of the interior of 

 Parheria may present no trace of the original coenenchyma 

 whatever except under section, when the lamina or wall of the 

 tubular structure is brought into view (figs. 5 and 6) . 



Where this has been tlie case the external or circumferential 

 part of the fossil has for some distance inwards been trans- 

 formed into a hard, compact, petrous shell, composed of a 

 dark black-brown (by transmitted light), waxy-looking mineral, 

 in which the remains of the coenenchyma may be faintly traced 

 together with filaments of the Millar ella (fig. 3, a). In short, 

 the whole looks like fossilized Mlllarella-structure ; but how- 

 ever this may be, on the inner side of this petrous portion 

 little holes begin to destroy its continuity, Av^hich soon trans- 

 forms it into the calcitized coenenchyma above mentioned 

 (fig. 3, J, c, and figs. 4, 5, 6) . In this case the latter, whose 

 interstices are empty, may occupy one third or more of the 

 interior of the Parheria, so that when the external or more 

 compact part of the specimen is cracked off the inner part of 

 the calcitized portion (fig. 3, c) falls out, like the kernel of a 

 nut under similar circumstances, when, from the interstices 

 being empty, it presents itself under the form of a spherical 

 ball of tubular reticulated thread-structure of a light brown 

 colour, identically representing a cast of the coenenchyma. It 

 was under this condition that I formerly made the mistake of 

 describing the skeletal structure of Parheria as being com- 



Ann. & Mag. N. Hist. Ser. 6. Vol ii. 4 



