i8o Shell Life 



become united to form a tube. There are two native 

 species : — 



The Elephant's-tusk Shell {Dentaliiimi entails) 

 whose white shell tapers, and curves slightly up- 

 wards, solid and smooth ; marked by the transverse 

 lines of growth, finely scratched longitudinally at 

 the narrow end, which is cut off" obli(|uely in mature 

 specimens and furnished with a tubular appendage. 

 It is also often notched at this end on the lower 

 (convex) side. The animal is white, the captacula 

 with oval tips, and the lobes of the foot scalloped 

 irregularly. It is found buried in sand at all depths 

 below 3 fathoms, usually in companies ; more plenti- 

 fully on tlie north than the south coasts. The 

 Grooved Tusk-shell (D. tarenti- 

 num) differs from the foregoing in 

 being a little shorter and stouter, 

 more solid, more curved, and with 



Grooved Tusk-shell i m c rrn i i 



a duller suriace. i\\q colour, too, 

 is a cream tint. The lines of growth are less evi- 

 dent as sculpture, but are sometimes indicated by 

 brownish coloration. The tubular appendage at the 

 smaller end is central ; there is no notch in the 

 shell, but the hinder half is regularly grooved longi- 

 tudinally as shown in the section above the accom- 

 panying figure. The animal has a yellowish tinge ; 

 the captacula are ringed and end in little disks ; and 

 the foot-lobes have a wavy margin. It occurs in 

 similar situations to the last, from extreme low water 

 to a depth of 25 fathoms. 



The Mail-shells {Chiton) introduce us to the class 

 Gasteropoda, to which all the Univalves belong. It 

 is a vast assemblage of orders, genera, and species. 



