452 APPENDIX II 



variety known as acorn-shells. They are found here, as eVery- 

 where, incrusting stones, wharves, shells, and other objects. The 

 body of the animal is surrounded by a shell, composed of six or 

 more plates, and in the shape of an irregular cone with the top 

 cut off; the base of the cone is attached to the object incrusted, 

 while the small end is closed by a shelly operculum which may be 

 opened at will. The feathery tentacles, which are modified feet, 

 are then extended and kept constantly waving. The smallest 

 species, Balanus balanoides, is the commonest, and is known as the 

 rock-barnacle. A large species, Coronula diadema, two inches in 

 diameter and with a very thick shell, lives on the surface of whales. 

 Balanus porcatus has been found fossil at Hopedale and Caribou 

 Island in beds of sandy clay and coarse gravel which are exposed 

 between tide-marks and extend beneath the water. 



It seems not inappropriate to include in our list two forms which 

 live in pools of fresh water close to the sea ; one of these is a schizo- 

 pod, Mysis relicta, which also inhabits Lake Superior, Lake Michigan, 

 and the lakes of northern Europe. It is so closely related to a 

 certain marine form as to suggest a common origin. At Indian 

 Tickle abound the "fairy shrimps," or branchiopods, in which the 

 gills or branchiae are situated on the feet, the eyes are large and 

 stalked, and the tail is long and slender. These shrimps are able 

 to live in pools which are dry for long periods, as the eggs, when 

 dried, preserve their vitality for an indefinite time. They swim 

 with the back downward, and the gills are bright orange. 



