332 Mr. CoNYBEARE on the Origin of a remarkable 



its fractured margin a range of hollow cellules will be observed 

 similar to those which in the earlier specimens have been occupied 

 by the infiltration of silex. In the present instance the specimen 

 has been imbedded in chalk only, and the removal of that soft sub- 

 stance has exposed the cellules in their empty state. 



I have assigned the succeeding figure (6.) to a very interesting 

 specimen, for the use of which I am indebted to Mr. Parkinson ; it 

 exhibits nearly the entire cast of a striated shell supposed by Mr. P. 

 to be similar to that which Walch has described under the name of 

 the Ostreo-Pinnite ; the shell in which this cast v/as formed, must 

 have become in places almost entirely cellular in its texture from 

 numerous perforations of the kind so often alluded to, since the in- 

 ferior margin of the upper valve is completely studded with a con- 

 geries of their globular casts of every size from that of the head of 

 the smallest pin to discs of the eighth part of an inch in diameter. 



Fig. 7. represents a very delicate groupe of minute globules, 

 which requires the assistance of a magnifying lens before its ana- 

 logy with the preceding specimens can be perceived. To the naked 

 eye it rather assumes the appearance of a coralloid ; a magnified 

 delineation of the same groupe is added, it is copied from a part of 

 a large white flint found at Heytesbury, in Wiltshire, over the sur- 

 face of which many such groupes are scattered, accompanied with 

 impressions of fragments of the striated shell described by Da Costa 

 as a patellite (Elements of Conchology, p. 142.) : it is the flatter 

 variety of the two which he describes, and it resembles that figured 

 by Mr. Parkinson. Organ. Rem. Vol. 3. PI. 5. fig- S. 



In all the preceding instances, the shells in which the cellules have 

 been originally formed, have belonged to one class of fossil shells, 

 the class (namely) which is distinguished by a striated texture 

 similar to that of the recent pinna marina. 



