52 LINNKAN GENERA. 



The shells of this g'enus iahabit the sea, lakes, and rivers. Those of the 

 ft^a in general adliereto rocks anJ stones ou tlie shore j and are so tenacious, 

 that they canno t be removed without breaking the shell, unless taken by- 

 surprise. Those inhabiting fresh water are generally found attached to 

 aquatic plants. The Patellae are called Limpets iu Britain. 



w Chamber. 



Genus 33.— DENTALIUM. 



Animal a Terebella ; shell univalve, tubular, straight or slight- 

 ly curved, wdth the cavity undivided, and open at both ends. 



Dentalium entalis.—TH]!: Tooth Dentaliuji. Plate IX, 

 fig. 33. White or yellowish, slightly ciu'ved, and tapering to a 

 fine point ; slightly striated. One and a-half inch long. Inha- 

 bits the British seas. 



The shells of this genus are only found in the ocean. They are solitary, 

 and lie in the mud, in an oblique or perpendicular position. 



Gemis 34.— SERPULA. 



Animal a Terebella ; shell univalve, tubular, generally ad- 

 hering to other substances ; often separated internally by divi- 

 sions at uncertain distances. 



Serpula vermicularis — The Worm- Like Serpula. Plate 

 IX. fig. 34. White, cylindrical, tapering, and variously curved 

 and twisted ; always affixed to other substances. Inhabits the 

 British seas. 



The Serpulae inhabit the ocean. They generally adhere to stones, shells, 

 and plants; sometimes a plurality of species are found on one stone or shell 

 There are also several species of Serpula which are unattached. 



Genus 35 TEREDO. 



Animal a Terebella, with two calcareous, hemispherical valves 

 cut off before, and two lanceolate ones : shell tapering, flexuous, 

 and capable of penetrating wood. 



Teredo navalis. — The Ship Teredo. Plate IX. fig. 35. 

 Cylindrical, taper ; smooth, white, and flexuous, finely striated 

 longitudinally. 



The shells of this genus inhabit the bottoms of ships ; and oak poles, which 

 are under water in harbours and docks. One species has been found in the 

 mud, at the bottom of the ocean. This last mentioned shell is the Teredo 

 Gigantea, and has been described to consist of a tube, five feet four inches in 

 length, nine inches in circumference at the larger, and two and one half 

 inches at the smaller end, and is the longest of all testaceous shells. 



