106 PAL/EON TOLOGY 



by ridges disposed more or less at right angles to the 

 aperture but without the steady parallelism of the spiral 

 ridges of a turreted shell : these ridges extend over the 

 edges of both lips, which are therefore said to be toothed. 

 Trivia is a genus of the family Cypr&idce, the Cowries. 

 The typical Cypraa is a tropical genus, which includes 

 the money-cowry and many large and richly coloured 

 species. It differs from Trivia in having the outer 

 surface of the shell smooth and polished by the deposit 

 of an extension of the inner layer by lobes of the mantle 

 which extend out and lap over it. In the youthful shell 

 the spire is visible though very short, and only as the 

 adult stage is reached does the shell become convolute. 



7. Fusus porrectus (Fig. 32), of the Barton Clay, is 

 a many-whorled, fusiform shell. The aperture is pear- 

 shaped, and is drawn out into a narrow, straight anterior 

 canal, nearly three times the length of the aperture itself. 

 The whorls are very convex in outline, ornamented by 

 nine spiral ridges of unequal strength, crossed by a large 

 number of varices (12 to a whorl except in some of the 

 earliest whorls) ; where they cross, the spiral ridges are 

 particularly prominent. In .the part of the last whorl 

 corresponding to the anterior canal (a part concealed in 

 the other whorls) the varices die away and the spiral 

 ridges are numerous and more uniform. If the shell is 

 perfect at the apex, the first two whorls are seen to 

 be quite different from the rest smooth and globose, 

 coiled on ah axis inclined at an angle to that of the rest 

 of the shell. This early stage, so markedly different 

 from the adult stage, is termed the nucleus or protoconch. 



