REPORT ON THE LAMELLIBRANCHIATA. 317 



1800 fathoms. Also Station 14G, Southern Ocean, east of j\Iarion Island, in 1375 

 fathoms. Also Station 302, west of Patagonia, in 1450 fathoms. 



The young of Amiissium dalli must approach very closely to this species. It may, 

 however, be distinguished on account of the more acute umbonal angles and the different 

 character of the surface structure of the left valve. 



The specimens fx"om Station 302 present one or two differences from those found at 

 the two other localities. The right or deep valve has some of the concentric lines of 

 growth elevated into slender Krse, which, crossing those radiating from the beak, produce 

 a distinctly cancellated surface. Besides this, the valves are strengthened with twelve 

 instead of eleven radiating lii-se. However, taking into consideration the exact 

 similarity of the microscopic sculpture of the left valve, I believe it advisable to 

 consider this form merely as a variety. It is most surprising to me that this species 

 could for an instant be considered as a variety of Amussium lucidum. Any one 

 holding such a view certainly must either be wanting in perceptive power or his 

 ideas respecting what are usually regarded as species be very peculiar. If any two 

 species of this genus are to be easily distinguished, those in question are they. 

 Amussium meridionale is larger, gapes on both sides, has both valves differently 

 sculptured, a shorter hinge-line, and the posterior auricle in the left valve is differently 

 sculptured. In specimens from a depth of 1000 fathoms, off the Azores, identified by 

 the late Dr. Gwyn Jeffreys as his Amussium lucidum, this ear has two or three radiating 

 ridges crossed by strong lines of growth, the former being wanting in Amussium 

 meridionale and the latter much finer. The Azorean examples also differ in being quite 

 closed at the sides. 



Amussium lucidum, (.Jeffreys) (PI. XXIV. figs. 2-2c). 



Pleuronectia lucida, JefiEreys, in Wyville Thomson, Depths of the Sea, p. 464, figs. 78, a, h. 

 Amussium lucidum, Jeffreys, Ann. and Mag. Nat. Hist., 1876, vol. xviii. p. 425. 

 Amussium lucidum, Jeffreys, Proc. ZooL Soc. Lond., 1879, p. 562. 



Habitat. — Station 73, west of Azores, in 1000 fathoms; Station 78, off San Miguel, 

 xlzores, also in 1000 fathoms; Station 120, off" Pernambuco, Brazil, at a depth of 675 

 fathoms. 



The Azorean specimens appear to differ in one respect from those originally described 

 by Jeffreys. The latter are said to have only nine internal supporting lirse, the figure, 

 however, in Thomson's book giving ten. In two valves in the British Museum I find 

 eleven, and in the Challenger examples usually fourteen, one or two of them occasionally 

 being only partially developed towards the outer margin. 



