NAIADITES MAGNA. 151 
8. NarapiTes MAGNA, sp. nov., Hind. Plate XIX, figs. 17—20. 
Specific Characters.—Shell moderately large, globosely subtriangular. The 
anterior end is somewhat compressed and almost obsolete, and has the same 
characters which obtain in other members of this genus. The anterior border is 
convex, meeting the superior border at an angle which is almost a right angle ; 
below it is produced downwards, joining insensibly the inferior border, which has 
a downward and posterior direction, sinuated in front and pierced for the byssus. 
Towards the posterior end the inferior border becomes deflected to the left, 
forming a shallow depression with the concavity looking towards the right, 
returning to the middle line at the posterior inferior angle, which is blunt and 
often the situation of a triple S-shaped folding, the sulci of which are to be traced 
upwards on the body of the posterior and lower part of the shell. The posterior 
border is truncate from above downwards and backwards, making an obtuse angle 
above with the superior border, and below is bluntly rounded in direction but folded. 
The hinge-line is straight, and extends the whole length of the superior border. 
The umbones are obtuse and swollen, at first directed inwards to the middle line, but 
before they reach it are bent sharply on themselves forwards, where they terminate 
on either side of the anterior superior angle; widely separated in casts, and 
only slightly raised above the hinge-line. From the umbones a very gibbose and 
broad oblique swelling, bounded in front by an almost obsolete oblique depression, 
passes downwards and backwards, becoming broader as it nears the margin, near 
which it becomes broken up into two or more ridges with intervening depressions, 
the ridges in the left valve being anterior to those in the right and opposite the 
depressions on the right valve. Above the oblique swelling the shell is rapidly 
compressed and expanded upwards into the posterior part of the hinge-line, so 
that the posterior slope of the shell is concave. The greatest convexity of the 
shell is only slightly below the hinge-line. The inequality of the valves is not so 
marked as in other species of this genus. 
The interior has a normal arrangement. Pallial line pitted, entire, and remote 
from the edge of the shell. The anterior muscular impressions are trifid, the 
most anterior being the largest. The position of the posterior adductor muscle 
has not been exposed. There is a shallow groove on each side of the median line, 
becoming deeper and broader posteriorly for the thickened lower margin of 
the hinge. 
Exterior.—The surface is almost smooth, and covered with fine striz and lines 
of growth; near the margin the lines of growth are closer, rougher, and more 
distinct. 
