448 Mr. H. J. Carter on the 



and typical structure in the central plane. D'Archiac's 

 specimen was evidently a more or less symmetrical fossil 

 with a central plane, since he states that it was susceptible of 

 being split into " equal parts/' which is not the case with 

 OrhitoUtes marginalis kc, as they present no " central 

 plane." 



Further I cannot go. D'Archiac's fossil is stated to have 

 come from E,oyan &c., and all seem to agree that the cliff at 

 Roy an on the northern side of the estuary of tlie Garonne 

 presents the " JMaestrichtien " of France, which is equivalent 

 to the Upper Chalk of Maestricht in the Netherlands. 



Lastly, I have to advert to the type of NummuUtes Man- 

 tellt, Morton, of 1834, viz. the Alabama species = OrhitoUtes 

 Mantelli, Cart. (1853), for the examination of which I am 

 again indebted to my kind friend Dr. H. Woodward ; and 

 here, for comparison, it is best to follow the same course 

 that I have taken with the Maestricht fossil. Thus : — 



The Alabama fossil is circular, flat, and thin, slightly 

 undulatory and smooth on the surface, presenting a small, 

 more or less gentle elevation in the centre, which is papilli- 

 form. Internal structure consisting of a central plane, in 

 which the cells or chambers in a horizontal section appear to 

 have been circular and situated respectively in the interstices 

 of intercrossing centrifugal lines, which, radiating from the 

 centre to the circumference in opposite directions, thus present 

 the " engine-turned " pattern to which I have alluded, and 

 in like manner show how the first-formed or central cells 

 become smaller and the circumferential ones largest, while in 

 the vertical section the same circumstances cause the central 

 plane to be thinnest in the centre and widest at the circum- 

 ference, towards which apparently the layers of cells running 

 into each other vertically cause the central plane in the ver- 

 tical direction to assume a series of curved lines whose con- 

 vexities are directed outwards. Central plane covered in on 

 each side by a convex crust composed of vertically compressed 

 cells separated only by fossilized shell-substance in which 

 there are no " columns ; " cells gradually losing their original 

 circularity outwards and becoming even still more compressed, 

 so as to present a reticulated appearance, in which the inter- 

 stices are extremely irregular both in form and size ; finally 

 concealed under a thin smooth layer of amorphous substance 

 which, where it has been chipped off, shows the subjacent 

 reticulation. 



Colour white, chalk-like, in accordance with the earthy 

 granular composition of the matrix in the hand-specimen, 

 which appears to consist chiefly of microscopic Foraminifera 



