MALACOZOA. TROFIOPODA. LAMELLIBRANCHIATA. 289 



gin ; the epidermis x r ery delicate, greyish-yellow ; the shell 

 yellowish-white, internally glossy, with the muscular impres- 

 sions faint. Length an inch, height seven-twelfths. 



Much more delicate, more elongated, and of a more yellow, 

 or yellowish-grey tint, than young individuals of Mactra 

 solida. 



Very abundant off Aberdeen, and frequently brought up by 

 the lines. 



Mactra elliptica. Brown, Illustr. Mactra elliptica. Forbes, 

 Malac. Mon. 48. 



4. Mactra subtruncdta. Small Triangular Mactra. 



Shell trigonal, inequilateral, rather thin, yellowish-grey or 

 greyish-white, with pale olivaceous epidermis ; the valves con- 

 vex, smoothish, with distant growth-lines ; the umbones pro- 

 minent, pointed, not central, the dorsal margin being shorter ; 

 both slopes obliquely striated ; the anterior end rounded, the 

 posterior angulate ; the inner surface glossy. Length an inch, 

 height ten-twelfths. 



Varies considerably in form and tint. 



Not uncommon along the sandy coasts ; often cast on the 

 beach, and young individuals frequently brought up by the 

 lines. 



Mactra stultorum. Penn. Brit. Zool. iv. 92. PI. 52. f. 42. Mac- 

 tra subtruncata. Mont. Test. Brit. 93. Mactra subtruncata. Penn. 

 Brit. Zool. Ed. n. iv. 194. PI. 55. f. 1 .Mactra subtruncata. Turt. 

 Brit. Biv. 70. Mactra subtruncata. Flem. Brit. Anira. 427. 

 Mactra deltoides. Lamk. Syst. v. 479; Ed. n. vi. 107. 



GENUS 2. GOODALLIA. 



Shell equivalve, inequilateral, trigonal, moderately con- 

 vex, closed at both ends. Umbones prominent. Hinge 

 strong ; one valve with a single central tooth, the other 

 with two teeth and an intermediate depressed space, for 

 the ligament ; lateral teeth elongated, with correspond- 

 ing grooves in the other valve. Muscular impressions 

 large, submarginal ; pallial impressions entire. 



1. Gooddllia trianguldris. Denticulate Goodallia. 



Shell trigonal, thick, opaque, smoothish, with some distant 

 growth-lines, dull white, with little gloss ; the umbones very 

 prominent, nearer the anterior end ; in one valve a prominent 

 2 B 



