INTRODUCTION. v 



remarkably rich in Microzoa. The Sponge-remains^ in this were described ten 

 years ago, and we now give in the Appendix (p. 54) a list of the Entomostraca 

 (Ostracoda), in which it will be seen a large majority of the entire number 

 of species known from the Upper Chalk is present. The Ostracoda, in common 

 with the other organisms in this material, are in beautiful preservation ; in many 

 instances both valves of the carapace are united together, and the delicate crenulated 

 fringes, tubercles, spines, &c., in numerous forms are uninjured. The specimens 

 are now of a dull, creamy- white tint, and nearly opaque ; and by treatment with 

 acid it is found that the carbonate of lime has been to a great extent replaced by 

 silica, for so treated the shell still retains its form in this mineral though it is now 

 snowy-white by reflected light, and nearly transparent by transmitted light when 

 mounted in Canada Balsam. A similar change has likewise taken place in the 

 Foraminifera in the same material. 



Norwich. — The Chalk of Thorpe, Whitlingham, and other places on the out- 

 skirts of the city, is on the same horizon as the beds at Horstead mentioned above, 

 but the Ostracoda obtained from it have been mostly from the Chalk itself, and 

 not from the interior of flints. The beds of Chalk near the surface in this dis- 

 trict have been in many places disturbed by glacial action, and the material is then 

 softened and the smaller organisms can be more readily washed out of it. The 

 list of species from Norwich is given at p. 54. 



Antrim, Londonderry, and Down. — The Chalk of these Counties in the North 

 of Ireland appears to be on the same geological horizon as that of Norwich and 

 Horstead — that is, in the zone of Belemnitella mucronata. In character, however, 

 it is very different, for instead of the soft earthy material with which we are 

 familiar in England, it has been indurated by the vast sheet of basalt by which it 

 is covered, and changed into a hard white limestone. As a consequence of this, 

 the Microzoa in it are not recognisable unless in thin sections. The Chalk, how- 

 ever, contains both the ordinary flints and large Paramoudras of precisely similar 

 character to those at Horstead, and the cavities in them are likewise filled with a 

 flint-meal rich in Foraminifera, Entomostraca, and Sponge-spicules. For this dis- 

 covery we are indebted to Mr, Joseph Wright, F.Gr.S., of Belfast,^ who, with cha- 

 racteristic energy, obtained samples of this material from thirty- six different localities 

 within the above-named Counties, and examined the Microzoa from each separately. 

 In addition to more than one hundred species and varieties of Foraminifera, there 

 were in the material seventeen species of Ostracoda determined by one of us. Six 

 of these forms appeared to be new, and provisional MS. names were given to them 



1 ' Fossil Sponge Spicules from the Upper Chalk, found in the Interior of a single Flint-stone 

 from Horstead, in Norfolk.' By G-. J. Hinde, F.G.S. 8vo. Munich, 1880. 



2 ' A List of the Cretaceous Microzoa of the North of Ireland,' by Joseph Wright, F.G.S., 'Sys- 

 tematic Lists, &c., Belfast Naturalist Field Club,' Appendix iii, 1875, pp. 73 — 99, pis. ii, iii. 



