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TURRITELLIDi*:. 



The British genera which we include in this family, 

 are Turritella and Coecum, very dissimilar in general 

 aspect, the former being regularly spiral, the latter, in 

 the state usually presented, uncoiled and tubular. Never- 

 theless, there are several points of affinity between the 

 shells, especially the separation of the apex from the rest of 

 the whorls as the creature advances in age, by a shelly 

 partition ; in Turritella^ the apex is persistent, and the 

 partition remains internal ; in Cmcum^ the apex is decidu- 

 ous, and the partition terminates the adult shell. The multi- 

 spiral structure of the operculum in each is an important 

 point of resemblance and characteristic of the tribe. 



The animals are, in several resjDects, nearly allied. 

 Their heads are similarly formed ; their eyes immersed at 

 the outer bases of the tentacula ; their sides not adorned 

 with filaments or fringes ; the operculigerous lobe simple ; 

 the foot very short in proportion to the body ; the 

 branchial plume single ; the sexes probably united. 



In many respects they have relations with Vermeius 

 and Slliquaria, which seem to belong to an intermediate 

 family conducting towards Scalaria and its allies. 



TURRITELLA, Lamarck. 



Shell spiral, turriculated, tapering, apex persistent, 

 whorls numerous, spirally grooved. Mouth with an entire 



