The animal is undoubtedly an Ascidia, and not a Tere- 

 belia, as ufually confidered. It is perfedlly fmooth through- 

 out, deftitute of any tentacula, feelers, or any appendages 

 whatever, not even the fmallefl: appearance of hmnchice, but 

 is hyaline, and purely fmiple in flru6lure externally, with 

 two tubes or fyphons at the fmaller end, placed between 

 two lanceolate teftaceous valves. 



The tubes are fimilar to thofe of other teftaceous Afcidia, 

 fimbriated at their ends, and are nearly divided to their ori- 

 gin at the jundlion of the auxiliary valves. Thefe tubes 

 are fmall, and capable of contra6ling within the valves, 

 which are intended for clofmg the entrance to the cell at 

 pleafure : through thefe tubes the animal takes in water, 

 and with it all nutriment, and like other Afcidia, ejects the 

 fluid again. 



It has no teeth or hard fubftance at the larger end, except 

 the fhells that protcdl: and cover it ; the opening, which is 

 fimilar to that of the animal of a Pholas, is fimple, firength- 

 ened only by an internal hyaline cartilaginous fubftance. 



With refpe(5t to the tefiaceous tube, which coats the ex- 

 cavations formed by thefe animals, there is fome difference 

 obferved in their ftrucSlure. 



In fome fpecimens of perfectly found oak timber, we 

 have feen thefe tubular cells fo crowded together, that the 

 animals appeared to have been conftrained to perforate each 

 others cell in thofe parts unprotected by the teftaceous con- 



B cretion : 



