116 MONOMYAIRA. 



violet coloured, with obscure radiations. Inhabits the Red 

 sea. 



TRIBE II MYTILACEA, 



Hinge with a subinterior marginal ligament, which is linear,, 

 very entire, and occupies a considerable portion of the anterior 

 margin ; shell rarely foliaceous. 



Genjis 27.— PINNA.— Zmn«u5. 



Generic Character. — Longitudinal, wedge-shaped, equivalve, 

 gaping at the base, and pointed at the summit, with the beaks 

 straight and acute ; hinge lateral and without teeth ; ligament 

 marginal, linear, very long, and half interior. 



Pinna ingens. — The Hoge Pinna. Plate XV. fig. 15. 

 Nearly triangular, horn-coloured, smooth, with distant folia- 

 tions ; striated on one side, with rough scaly wrinkles on the 

 broader end. Twelve inches long. Inhabits the coast of 

 Britain. 



Genus 28.— M YTIL US.— Linmius. 



Generic Character. — Longitudinal, equivalve ; apex acute, 

 affixed by a byssus ; beaks acute, nearly straight and terminal; 

 hinge lateral, generally without teeth; ligament marginal, and 

 partly internal ; muscular impressions elongated, clavate, and 

 sublateral. 



Soction * Longitudinally furrowed. ** Without furrows. 



Mytilus edulis.— The Edible Mytilus. Plate XV. fig. 16. 

 Oblong-oval, nearly smooth, pointed and slightly carinated at 

 the beak, truncated on one side, and dilated on the other ; cov- 

 ered with an olivaceous epidermis ; beneath which it is radiated 

 with blue or purple ; internal margin blue, the concave part 

 white. Two to three inches long. Inhabits the British seas. 



Genus 29.— MODIGLA.— Lamarck. 



Generic Character. — Subtranswerse, equivalve, regular; the 

 posterior side very short ; beaks nearly lateral ; hinge without 



