44 CORBULIDvE. 



with a single erect cardinal tooth in one valve or both, besides 

 a long lateral tooth on one or each side in either valve ; in 

 species of Necera there is also a free calcareous ossicle : pallial 

 scar slight, with a shallow sinus : muscular scars well marked. 



These are of small size, and comprised in few genera : 

 the species are numerous and prolific, characters which 

 are probably correlative. The British genera are Poro- 

 mya y Necera, and Corbula. The first is a box studded 

 with tiny pearls. 



" Ne lesse praisworthie faire Nesera is." 



Her shell resembles the body of a bird, without 

 feet or wings, but having a stretched-out beak ; and, 

 although this age is not barren of artistic invention, 

 it might serve as a graceful model for some work of 

 fictile manufacture. The last has also an apposite 

 name, and reminds one of a basket with a close-fitting 

 lid. The hinge in each genus is constructed somewhat 

 on the plan of the Mactridae ; but it does not possess 

 an external ligament as well as an internal cartilage. 

 The Corbulida live in mud and sand at various depths, 

 but seldom between tide-marks. Lamarck called them 

 "Corbulees," Latreille "Corbulsea," and Hinds "Cor- 

 bulacea." 



Genus I. POROMT A*, Forbes. PL II. f. 3. 



BODY roundish-oval, thin : tubes unequal in size, clothed 

 with numerous long filaments : foot narrow and slender. 



SHELL roundish-oval, slightly inequivalve and inequilateral, 

 thin and pearly, with the outer layer composed of minute 

 tubercles ; posterior side angulated : epidermis membranous 

 and thin : teeth, in the right valve a short but strong cardinal, 

 and in the left a minute triangular cardinal and a ridge-like 

 lateral on the posterior side. 



* Passing into the genus Mya ; or having, with the shape of that shell, 

 a tubular structure. 



