240 MALACOZOA. TROPIOPODA. LAMELLIBRANC'HIATA, 



dorsal margin of the shell, which is straight, the an- 

 terior margin obsolete, anterior inferior much produced 

 and nearly straight, inferior rounded. 



1. Pinna ingens. Great Fan-Mussel. 



Shell obovato-triangular, moderately convex ; with the 

 dorsal line straight for more than half its length, then rounded ; 

 the anterior ventral line sinuate, the posterior rounded; the 

 valves thin, semitransparent, greenish-grey, or dusky, with 

 several longitudinal narrow obtuse ridges on the half next the 

 ligament, and transverse striae, which become more promi- 

 nent, irregular and undulated, on curving along the inferior 

 side; the ribs obsolete or terminating toward the broader 

 rounded extremity, where the transverse striae are laminar or 

 scaly ; inside shining, with a thin, pearly and iridescent layer. 

 Length about ten inches, breadth toward the end six. 



In young individuals the shell is thin, semitransparent, and 

 yellowish-green. There is great difference in the form of in- 

 dividuals, some being oblongo-triangular, others obovate. 



In deep water, on a hard bottom, off Aberdeen ; not very 

 unfrequently brought up by the lines. In the Winter of 

 1841-42, half-a-dozen specimens were obtained by my pupils, 

 one of them with the animal alive. In October, 1842, Mr. 

 Murray obtained for me, at Fraserburgh, a specimen a foot 

 long, which had been taken up at the distance of forty miles 

 from land. 



Pinna ingens. Penn. Brit. Zool. iv. 1 15 ? Pinna fragilis. Penn. 

 Brit. Zool. iv. 115? Pinna ingens. Mont. Test. Brit. 180. Pinna 

 ingens. Flem. Brit. Anim. 406. Pinna ingens. Lamk. Syst. vi. 

 134; Ed. 2. vii. 66. Pinna ingens. Turton, Brit. Biv. 221. PI. 

 20. f. 1. Pinna fragilis. Turton, Brit. Biv. 222. PI. 20. f. 2. 



FAMILY III. UNIONINA. 



Animal oblong, ovate, elliptical, or roundish ; with 

 the mantle open beneath, coherent behind, and forming 

 two orifices, the upper small and simple, the lower large 

 and barbate on the margin ; a large compressed, taper- 

 ing foot ; two adductor muscles, both large, widely se- 

 parated. 



Shell regular, equivalve, inequilateral, covered with a 

 hard laminated epidermis ; the hinge toothless, or with 

 irregular teeth ; the ligament linear, dorsal, external ; 



