which are given in the accompanying- plates, I am in- 

 debted to Herr Conrad Schwager, Assistant in the 

 Palaeontological Museum at Munich, who, at very short 

 notice, kindly undertook the task of drawing and li- 

 thographing them. As far as possible the figures 

 have been drawn to the same scale of 20 diameters, 

 in order to enable theirhrelative dimensions to be ap- 

 preciated. In a few instances, in which a larger 

 scale has had to be adopted, a representation of the 

 object is also given, where practicable, on the same 

 scale as the other spicules. In comparing the fig- 

 ures given in these plates with those of similar spicules 

 which are given in the beautiful illustrations of Prof. 

 Zittel's work on Coeloptychium and in Mr. Carter's fig- 

 ures of the spicules from the Haldon Green Sand, it is 

 very necessary to bear in mind the different scale to 

 which these figures have been drawn. In Professor 

 Zittel's work the detached spicules on the Plates IY-VII 

 are represented one hundred times magnified, and thus 

 five times larger than in my Plates, and the Haldon 

 spicules are drawn to the scale of seventy-five diame- 

 ters or three and a half times larger. Bearing this 

 fact in mind it will be noticed that most of the spi- 

 cules from the Horstead chalk are actually larger than 

 those from Germany and the South- West of England. 

 I may add that the accuracy of the drawings of the 

 Horstead spicules is further assured by their having 

 been done by means of the Camera lucida. 



Palaeontological Museum Munich. 



November 1880. 



