MOLLUSCA. 319 



them are minute, and although they are numerous, few of those in 

 our seas have been observed, and very few have been satisfacto- 

 rily made out. The largest, and the only ones of much magnitude, 

 are the two following : 



AsCi'DIA RU'STICA, LIN.; Encyc. Mtth., pi. C2, f. 7-U. LAM.; An. 

 sans Vert., iii. 528. 



It is found of all sizes, from that of a pea to that of an olive, 

 adhering in clusters to floating timbers, to stones, corals, &c. It 

 may always be found in abundance on the under side of logs in 

 the timber-docks about Boston. It is usually of a globular form, 

 but more or less irregular in shape and in the degree of smooth- 

 ness of its surface, and in substance is much like crude india- 

 rubber. It is usually invested with plants or particles of earth ; 

 but, when clean, it is rust-colored. It has two small orifices, near 

 each other, through which a jet of water is projected, whenever 

 a touch induces the animal to contract. I am not aware that it is 

 in any way injurious to man. 



BoLTE^NIA RENIFO'RMIS, MAC LEAY; Lin. Trans, xiv. 536, pi. 18. 

 Ascidia globifera, SABIXE ; Append, to Parry's Voy. No 10. Ascidia clavata, FABR. ; 

 Fauna Grcenl., 333. LAM.; Jin. sans Vert., iii. 539. 



This is a most curious object, and greatly resembles in shape 

 the flower of Ladies-slipper (Cypripedium) on its stalk. It has 

 a kidney-shaped body, of a wrinkled, leathery structure, about 

 two inches long and one in width, suddenly narrowing at the top 

 into a small stalk not larger than a crow-quill, and from six to 

 twelve inches in length. It has two cross-shaped orifices, nearly 

 an inch apart. It is attached by its stalk to stones in deep water, 

 whence it is occasionally hooked up by the fishermen, or driven 

 on shore by storms. Its surface is usually loaded with marine 

 plants, zoophytes, &c. 



The other animals of this class are mostly minute, living in 

 communities, and incrusting stones, marine plants, &c., with a 

 gelatinous substance which affords them a common residence. 

 Such are the various species of Aplidium, Polyclinum, and Bo- 



