l8: 
over the ends of the basal rays, or it may be regularly curved in its lateral thirds but nearly 
straight in its median tliird ; liie middle of the dorsal surface of the IBr, is occupied by a large 
prominent broadly oval well rounded tubercle; the axillaries are broadly rhombic with the 
lateral angles truncated so that the lateral edges 
are from one half to two thirds the length of 
the sides of the IBr,, two and one half times as 
broad as li>ng, in the median line nearly twice 
as long as the lP)r, ; the centre, except at the 
anterior angle, is occupied by a tubercle which 
is more elongated dorsoventrally than that on 
the IHr, and, though as high, less prominent as 
it rises much less abruijtly; the lateral edges 
of the 11 'ir, and the IBr., are turned slightly 
outward; the lateral thirds of the proximal edge 
of the axillaries and the corresponding portions 
of the distal edge of the IBr, are also turned 
upward to the same height as the lateral edges; 
the eversion of the latter is most marked just 
over the ends of the basal rays and gradually 
decreases anteriorly to the distal corner of the 
lateral edge of the axillary; it is continued thence 
along the sides of the fu'st four brachials ; the 
inner lateral edges of the first five brachials are 
similarly modified. 
The arms are, in the type, 165 mm. long. 
The first brachial is wedge-shaped, slightly 
longer exteriorly than interiorly, twice as broad 
as the exterior length ; the proximal border is 
narrowly produced ; the outer border is produced 
like the lateral borders of the axillaries; the 
inner border is similarly produced, especially at 
the distal angle, which is more or less rounded 
off and overlaps the proximal inner angles of 
the second brachial. The second brachial is about 
the size and shape of the first, with the outer 
edge .similarly produced ; the production of the 
inner edge is like that of the outer, but not so 
i-ig. 7. 
Lateral view of a specimen of Perissomttra tinior/ntit from 
Stat, 297. Natural size. (Courtesy of the t'. S. National Museum). 
marked. The third and fourth brachials form a 
syzygial pair which is oblong, about twice as 
broad as long, with the lateral edges turned outward as in the brachials preceding; the following 
brachials are slightly wedge-shaped, about twice as broad as long; one brachial between the 
