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 substance 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 was formed, must have become in places almost entirely cellular in its texture from numerous perforations of the kind so often alluded to, since the inferior margin of the upper valve is completely studded with a congeries 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 analogy 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 surface 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. Pl. 5. fig. 3.
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.
