MOLLUSCS, OR SHELL-FISH. 



247 



(6) Siphonate forms. 



Spire sharp- \ 

 pointed, canal r 

 narrow . . ' 

 Spire short, \ 

 Shell oval, spir- canal short j 

 ally sculp- I and recurved, I 

 tured, canal \ columellaj 

 short . . with fold at I 

 base . . J 

 Spire blunt, -\ 

 canal open j- 

 and deep . J 

 Shell spindle- ] f 



shaped, with I 

 long straight ( FuSUS ' '] 

 canal . / I 



Shell with con- \ 



r p re SP 4 ^~^" 



Purpura lapillus, shell white or 

 banded. 



N. reticulata, 

 shell large. 



N. incrassata, 

 shell small, 

 aperture much 

 narrowed. 



Nassa 



Buccinum undatum 

 dulated. 



shell un- 



F. antiquus, strise numerous, body- 

 whorl wide. 



F. islandicus, strise few, body- 

 whorl narrow. 



For (3) GASTERoroDA OPISTHOBRANCHIA, see next chapter. 



NOTE ON DISTRIBUTION. 



From the great multitude of shell-bearing Gasteropods we have 

 been able to pick out relatively so few that not much can be profit- 

 ably said as regards the distribution generally. Most of the forms 

 mentioned occur all round the coast. The whelks lusus islandicus 

 and Buccinum undatum may be mentioned as forms commoner in 

 the North than in the South, while the cowry (Cyprea) is an example 

 of one commoner on the South and West, at least between tide- 

 marks, than on the East Coast. We have already indicated that 

 although the pretty tortoise-shell limpet is absent from the South 

 and West, its absence is atoned for by many other curious and 

 interesting forms. A similar replacement of species occurs among 

 other genera. Thus at Lynmouth, on the north coast of Devon, the 

 common grey top ( T. cinerarius) appeared to be absent, but the pools 

 were filled with two other species a small one prettily marked with 

 brown (T. umbilicatus), and a larger dark-coloured one (T. lineatus). 

 But, allowing for such cases, it may be said generally that the 

 Gasteropods which are hardy enough to live between tide-marks are 

 also hardy enough to live all around our coasts. 



