240 MALACOZOA. TROriOPODA. LAMELLIBRANCIIIATA* 



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 

 unfrecmently 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. Perm. Brit. Zool. iv. 115? 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 ; 



