2 EDGAR A. SMITH. 
is more minutely perforated all over, the foramen is smaller, and on each side of it the 
valve (the ventral) exhibits a more or less distinct keel ; also the internal septum of the 
dorsal valve is stronger and longer. The present species is perhaps more closely 
related to M. kerguelenensis, but, besides being thinner and more conspicuously 
perforated, it does not exhibit the mesial depression referred to in the description of 
that species; the foramen also is larger. The internal septum is equally thin and 
delicate. The form is somewhat variable, some specimens being broader than others. 
The colour is light brown, or dirty horn-colour. 
Largest specimen.—Length, 43°5 millim. ; width, 39; diam., 24. 
Another example.—Length, 37:5 millim. ; width, 29°5; diam., 22:5. 
Agassiz Island, 300 fathoms, mud, off ice barrier. 
A few more or less damaged specimens were obtained. 
MaGELLANIA suLcaTa. (Figs. 3, 4.) 
Shell of medium size, ovate, globose, of thin substance, horn-colour, inequivalve, 
exhibiting, excepting towards the umbones, numerous concentric conspicuous raised 
lines of growth, producing a remarkable sulcate appearance; dorsal valve less convex 
than the ventral, which is produced and curves over so that the foramen, of moderate 
size and circular, is on a plane with the margin of the valve and separated from the 
edge by a narrow deltidium; interior of the valve concentrically sulcate like the 
exterior ; teeth of ventral valve moderately strong ; loop very thin and delicate, broad 
and reflexed, with a thin acute septum beneath, extending half-way across the valve, 
with the crural points long and acute; perforations of the test large, oblong. 
Length, 28 millim. ; width, 23; diam., 17. 
Coulman Island, 100 fathoms, and Winter Quarters, August 7, 1902, 178 fathoms. 
This species is remarkable on account of the concentric sulcations and the coarse 
perforations of the shell. I do not know of any recent form that exhibits sulci or 
marked lines of growth of this kind, but among fossil forms a similar kind of surface 
ornamentation is met with in Terebratula sulcifera, Morris, of the lower chalk. 
