244 MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 



and convex ; the hinge with twenty, erect, compressed, obtuse 

 teeth on the dorsal margin, ten on the anterior ; the inner 

 surface pearly and shining ; the margin crenulate. Length 

 six-twelfths, height five-twelfths. 



Young shells are more elongated, paler, almost white, with 

 the inner surface iridescent. 



Common off Aberdeen, Peterhead, and Banff, and fre- 

 quently brought up by the lines. 



Area Nucleus. Linn. Syst. Nas. i. 1143. Nucula Nucleus. 

 Turt. Brit. Biv. 176. PI. 13. f. 4. Nucula Nuclea. Flem. Brit 

 Anim. 401. Area Nucleus. Mont. Test. Brit. 141. Nucula mar- 

 garitacea. Lamk. Syst. vi. 59 ; Ed. 2. vi. 506. 



2. Nueula tennis. Thin Nucule. 



Shell obliquely ovate, compressed, glossy, smoothish, obso- 

 letely striated transversely, with distinct growth-lines, and 

 extremely faint indications of minute longitudinal striae, the 

 epidermis yellowish-green ; the umbones rather prominent, 

 small ; the anterior slope abruptly descending, convex, with 

 a large ovato-oblong impression, the dorsal slope elongated, 

 convex, the posterior extremity somewhat angulate ; the hinge 

 with twelve erect, slightly recurved, compressed teeth on the 

 dorsal margin, five on the anterior ; the inner surface some- 

 what pearly, highly iridescent, reflecting the most lively tints 

 of purple, green, and blue, in zones; the margins entire. 

 Length six-twelfths, height four and a-half. 



Young shells are more elongated, paler, and semitrans- 

 parent. More elongated, more compressed, and thinner than 

 Nucula Nucleus, and further distinguished by having the mar- 

 gin not crenulate. 



Not very uncommon off Aberdeen, and sometimes brought 

 up by the lines. 



Area tenuis. Mont, Test. Brit, Suppl. 56. PI. 29. f. 1. Nucula 

 tenuis. Turt. Brit. Biv. 177. Nucula tenuis, Flem. Brit. Anim. 

 402. 



3. Nucula rostrdta. Beaked Nucule. 



Shell elongated, oblongo-lanceolate, moderately convex, 

 thin, concentrically striated, with the posterior end rounded, 

 the anterior extended, narrowed, and truncate ; the surface of 

 the shell whitish, the epidermis yellowish-grey ; the umbones 

 very small, scarcely curved; the cardinal teeth compressed, 

 pointed, oblique, twenty on one side, eighteen on the other ; 



