114 MONOMYAIRA. 



ligament marginal, partly linear, and either simple or interrupted 

 by crenulations. 



Genus 22.— MELEAGRINA.— Xamarc;^. 



Generic Character. — Somewhat equivalve, rounded and scaly 

 on the outside : a sinus at the posterior side of the shell for the 

 passage of the byssus, at which place the left valve is notched 

 and narrow •, hinge linear, and destitute of teeth ; ligament 

 marginal, elongated, and placed nearly exterior, and dilated in 

 the centre. 



In many respects resembling the Avicula, but difiFering in being- equivalve, 

 and always witliout the elongated transverse base, on the cardinal tooth. 

 The sloping sides of the opening, admitting the passage of the byssus, is per- 

 ceptible on both valves, which is never the case with the Avicula, where a 

 notch answers the same purpose. 



Meleagrina margaritifera. —The Pearl- Be aringMeleagrina. 

 Plate XV. fig. 10. Som.ewhat square, compressed ; undulated, 

 and transversely striated, with a series of lamellated longitudinal 

 scales ; greenish on the outside and pearlaceous within. Ten 

 or twelve inches long. Inhabits the Indian ocean. 



Genus 23. — AVICULA — Lamarck. 



Generic Character. — Shell inequivalve, fragile, with the top 

 straight, transverse, and produced at both extremities, the ante- 

 rior of which is caudiform ; valves oblique ; the left one emar- 

 ginate, with a sinus or notch, through which the byssus passes ; 

 hinge linear, with one tooth in each valve, under the beaks ; 

 ligament linear and marginal, placed in a long narrow groove. 



Avicula Anglica. — The English Avicula. Plate XV. fig. 

 11. Wing moderate, obliquely curved ; yellowish fawn-coloured, 

 with dark reddish-brown blotches ; inside pearlaceous and irides- 

 cent. One inch and a fourth long. Inhabits the Devonshire 

 coast. 



Genus 24.— MALLEUS.— Za/narcA. 



Generic Character. — Subequi valve, rugged, distorted, fre- 

 quently elongated ; sublobate at the top ; beaks small, diverging ; 

 hinge without teeth, with an elongated conical furrow under the 



