110 MONOMYAIRA. 



Jnomia undulafa. — The Waved Anomia. Plate XIV. fig. 

 2. Suborbicular, pellucid, with strong, irregular, undulated, 

 longitudinal striae, and some transverse concentric ones ; outside 

 yellowish dirty green ; inside fine green ; the ligament perfora- 

 tion large, ovate ; muscular impression star-shaped. Two inches 

 broad. Inhabits the British coasts. 



Genus U — PL AC UNA.— Zamarc^. 



Generic Character. — Shell free, subequivalve, irregular, very 

 flat ; hinge interior, with two short longitudinal convergent ribs, 

 in the form of the letter V, and divaricated beneath, which fit 

 into two grooves in the opposite valve, held together by the liga- 

 ment. 



Placuna placenta. — The Placenta Placuna. Plate XIV. 

 fig. 3. Suborbicular, flat, white, and pellucid, with fine longitudi- 

 nal strisB, slightly decussated. Four inches long. Inhabits the 

 coasts of China. 



** Shell foliaceous, frequently ponderous, with a semi-in- 

 terior ligament. 



Genus 12,— VULSELLA Lamarck. 



Generic Character. — Longitudinal, subequi valve, irregular, 

 and free ; umbones equal ; hinge, with a projecting callosity de- 

 pressed above, and a conical oblique hollow for the ligament ; 

 within each valve is a lengthened muscular impression. 



Vulsella lingulata. — The Latchet Vulsella. Plate XIV. 

 fig. 4. Elongated, depressed, transversely striated ; pale yel- 

 lowish brown, with longitudinal darker stripes. Four inches 

 long. Inhabits the Indian ocean. 



Genus 13 OSTREA Linnaus. 



Generic Character. — Shell adhering to extraneous bodies ; in- 

 equivalve and irregular, with the beaks separated, and the up- 

 per valve advanced as the animal enlarges ; hinge without teeth ; 



