64 BIVALVES. — OSTREA. 



The common oyster (O. edulis) is too well known for 

 its nutritious and palatable properties to require much de- 

 scription ; suffice it to say, that the exterior of the shell is 

 usually covered with undulated and imbricated scales, of 

 a yellowish or pinkish olive cast ; and the old shells are of- 

 ten covered with various adhesions, such as anomice, ser- 

 pulae, lepades, sertularise, and other marine productions. 

 The interior of the shell has generally a pearly appearance, 

 and specimens are often found containing pearls. They 

 are to be met with in most seas, occasionally in clusters, 

 affixed to rocks and other substances. In some places they 

 are considered so profitable a branch of traffic, that the 

 greatest care is taken to promote their generation and 

 growth. By proper management their multiplication be- 

 comes immense. They are often formed into large layers 

 or beds, extending many miles ; which, in favourable sea- 

 sons, prove a submarine mine of wealth to their propri- 

 etors. 



Ostrese are found in every part of the world; but the 

 most rare are produced in the Indian seas. 



OSTREA— Oi/s/er or Scallop. 



Division I. — Valves with ears equal. 



Family 1. — Valves ribbed, tipper valve flat. 

 * Maxima — Greatest. Ziczac — Zigzag. 



♦Jacobsea — Lesser. Striatula — Siocteen-rayed. 



Minuta — Minute. 



Family 2. — Valves ribbed, ears equal. 

 Hybrida — Hybrid. Imbricata — Imbricated. 



Radula — Rasp. Plica — Folded. 



Hians — Gaping, 



Family 3. — Valves flattish on 07ie side and gaping. 

 Lima — File. *Fasciata — Banded. 



