UNIVALVES. — SABELLA. 147 



seminal vessels of the xilosteum granatum ; one end is cla- 

 vate, the other incurved, narrower, obtuse, and perforated 

 in the middle : the shell is rough, and brownish on the out- 

 side, but within it is smooth, and more or less flexuous. 

 It is nearly two inches long, but not half an inch wide. 

 The fourth is the T. gigantea, which is remarkable for hav- 

 ing its interior separated by imperforated convex and con- 

 cave divisions, making the shell appear as if it consisted of 

 numerous united tubes. The smaller end of this shell is 

 also peculiar for being terminated by two distinct or se- 

 parate small tubular pipes, which are jointed in the same 

 manner as the main stem from which they spring; the 

 shell, in this state, resembles a two-pronged fork. It is 

 an inhabitant of the Mediterranean and Indian seas, and 

 is often found concealed under the sands; it sometimes at- 

 tains the extraordinary size of three feet 



TEREDO— *S/ii;j Worm, 



Navalis — Ship. Clava — Club-shaped. 



Utriculus — Timber. Gigantea — Gigantic. 



SABELLA.-- -Sabella. 



Animal — a Nereis, with a ringent mouth, and two thicker 

 tentacula behind the head: Shell tubular, composed of 

 particles of sand, broken shells, and vegetable substances, 

 united to a membrane by a glutinous cement. 

 THIS very extraordinary genus contains no less than 



twenty-five species. The membrane which composes the 

 h2 



