114 UNIVALVES. SERPULA. 



or twined into all sorts of spiral and grotesque figures: 

 some, on the contrary, are nearly straight, and consist of 

 a single tube ; whilst others are collected into large mas- 

 ses, containing many hundred spiral and twisted tubes, 

 curiously interwoven or interlaced with each other. 



Amongst those species which are spiral and single (hav- 

 ing their whorls nearly contiguous, something like a He- 

 lix) may be included the Serpula Spirillum, SerpulaSpi- 

 rorbis, and Serpula Afra. 



Those species that are single, and nearly straight, are 

 the following: viz. Serpula Protensa, and Serpula Poly- 

 thalamia. The latter of which most probably belongs 

 to the genus Teredo; it is remarkable for having its 

 interior separated by imperforate, convex, and concave 

 divisions, making the shell appear as if it consisted of nu- 

 merous united tubes. The smaller end of this shell is also 

 peculiar for being terminated by two distinct or separate 

 small tubular pipes, which are jointed in the same man- 

 ner as the main stem from which they spring; the shell, 

 in this state, looks something like a two-pronged fork. 

 It is an inhabitant of the Mediterranean and Indian seas, 

 and is often found concealed under the sands; it some- 

 times arrives at the extraordinary size of three feet. 



To this same division belongs the well known but rare 

 shell, the Watering-pot Serpula. The larger end of this 

 shell is closed by a convex disk, which is beset with nu- 

 merous small perforations, and a longitudinal one in the 

 middle, the whole encircled by a dilated margin of ele- 

 gant papyraceous tubes, exactly resembling a beautifully 

 plaited ruff or frill; the smaller end is open. In point of 

 size, it seldom exceeds five inches. The Indian ocean is 

 its birth place, and, when perfect, it is highly valued. 



