172 TURRITELLIDiE. 



suborbiciilar, or slightl}- angulateil peritreme, outer lip 

 tliiii. Operculum corueous, multispinil, fimbriated at its 

 edges. 



Animal with a muzzle-sliapecl head, bearing two long- 

 subulate tentacles, having eyes on their external bases, 

 slightly prominent. Foot very short in proportion to 

 the shell, truncate in front, rounded behind, grooved 

 beneath. Opercular lobe occupying the caudal disk, not 

 cirrhated nor winged. Mantle with a fringed margin, 

 obscurely siphonated at the right side. Branchial plume 

 single, very long. Tongue very short ; each scries of 

 denticles consisting of a subquadrate median, with an 

 incurved denticulated apex, and of three similar ligulate 

 uncini on each side, all with hamate serrulated summits. 



This genus appears to be distributed, though sparingly, 

 all over the world. More than fifty species have been 

 described and figured. The majority are inhabitants of 

 the Laminarian zone, from whence they are often cast on 

 shore by the waves, but several range to great depths. 

 Fossil species date with certainty far back into the 

 secondary period. The genus appears to have had its 

 maximum of development during Older Tertiary times. 



The animal of Turritella, when full grown, does not 

 fill up the entire length of the shell, but partitions off, as it 

 were, part of its spire. 



T. COMMUNIS, llisso. 



Plato LXXXIX. fig. 1, 2, 3 ; and (animal) Plate I. T. fig. 4. 



Li.si'Eii, Anim. Aiigl. pi. ?>., f. H. 

 Turbu icrebra, LiNN. Syst. Nat. ed. 12, p. 1239 (only a small part); Fauna 

 Succica, p. 52.5. — Pknn. Brit. Zool. ed. 4, vol. iv. p. 130, pi. 81, 



f. 1 13 Mont. Test. Brit. vol. ii. p. 293. — M.xton and Hack. 



'i'ranB. Linn. Soc. vol. viii. p. 1 7(). — Rack. Dorset Catalog, p. 51 , 



