46 THE SIIKLL-FJSII OF THE COAST. 



dry (luring low-water. One or more forms grow 

 on the roots of trees, such as the mangrove, on 

 which they remain exposed for hours at a time 

 above water. The great thickness of the shell in 

 many individuals indicates a long life-period for 

 the animal, which has been estimated by some, but 

 probably without sufficient basis, to he as much as 

 a hundred years. The difterent layers of the shell 

 indicate distinct periods of rest in its develop- 

 ment, but at what regular (if regular) intervals 

 these periods follow one another is still an open 

 question. In the east-coast oysters, whoso most 

 extensive head-quarters appear to be Chesapeake 

 Bay, the shell rarely attains a greater length than 

 one foot or 15 inches; but foreign and fossil species 

 are known which far exceed these dimensions. 

 Thus, a species from the Middle Tertiary deposits 

 of Europe {Osirca crassissima) measures nearly or 

 fully two feet in length; the Osirca Titan, from a 

 somewhat later deposit in California, measures six 

 inches through the thickness of the two valves, 

 while a recent species (0. Talienwanensis), from the 

 Bay of Taichou, Japan, grows to a length of even 

 three feet. Careful investigation has shown that 

 the American oyster will grow to a length of 

 nearly four inches in about two years, and it is 

 conjectured from this that in some four years after 

 its escape from the egg the animal is approximately 

 adult and marketable. 



Oysters appear to thrive best in estnarine coves 

 and inlets where the bottom is not liable to shift 

 to any great extent, and where the depth of water 



