[dyer] CONULARIA RUGOSA 67 



Considerable variation in detail is observed in different parts of 

 the shell. In the first place the spacing of the ridges and grooves 

 varies from ten in a centimetre near the aperture to twenty in the 

 same distance near the apex. Another variation is seen in the 

 character of the ridge; in some parts of the shell (PI. II, Fig. 1) it is 

 sharply defined, with square edges, and with a continuous depression 

 along its centre which expands at intervals to oval scars. In other 

 parts (PI. II, Fig. 2) the ridges are more rounded and are marked 

 by elevated papillae in place of the depressed scars. These papillae 

 are apparently hollow as minute apertures are observed at their 

 summits in some instances. 



Beside the outside wall itself the impression of the outside wall 

 is also seen. This impression is clearly made by the type of orna- 

 mentation seen in PI. II, Fig. 2. Wide, rounded, transverse ridges 

 are separated by narrow grooves. The ridges are marked by rounded, 

 longitudinal elevations and depressions. In the transverse grooves 

 deep punctures are found lying opposite the longitudinal depressions. 



The greatest length of- the shell is 95 millimetres and the greatest 

 width of one face is 42 millimetres. 



Our specimen agrees with Spencer's type in size and shape. 

 The apical angles are approximately the same in both specimens. 

 The angle made by the transverse ridges as they meet to form the 

 line in the middle of each face is also approximately the same. The 

 type of ornamentation which Spencer figures, and which is said by 

 him to characterize the internal cast of the shell, is very similar to the 

 ornamentation observed on the external impression of our shell. The 

 true surface of the shell, however, was not found by him and is de- 

 scribed in this article for the first time. 



—36 



