ARCA. 328 



the depth of six fathoms, off San Xicholas, one of the Phi- 

 lippines. A pretty little species, named by Mr. Eeeve the 

 Avicula Ark {A. avictcloides) , was found in like manner at 

 St. Helena, in a muddy bed ten fathoms deep. "Wliite 

 coral, in the harbour of ^Mozambique, formed the dwelling of 

 the Hankey iVrk, A. Ilmikeyana, thus named in compliment 

 to Lieut. Hankey, E.N., a zealous conchologist, whose re- 

 searches on the coast of Africa have greatly contributed to 

 the advancement of science ; while the beautiful Pacific Arks 

 {A. Pacifica) are found adhering to one another in bunches, 

 and attached to rocky ground at the depth of from six to 

 eighteen fathoms, at St. Elena, South America. Strong 

 ribbing, and wing-like expansions of the posterior side, 

 characterize this beautiful species. Others are found con- 

 cealed beneath stones or attached to shells, and one species, 

 the Lithodomus-Yik.Q Ark {A. Lithodomus) , most probably be- 

 comes imbedded in stones and rocky masses, by the aid of 

 some powerful solvent secretion. 



The delicately-sculptured Decussated xirk {A. decussata) 

 in which the epidermis rises from between the striae in scaly 

 bristles, attaches himself to shells in the Pacific Ocean, and is 

 found especially at the Philippines, and Lord tlood's and 

 the Chain Islands. 



