640 THE VOYAGE OF H.M.S. CHALLENGER. 
muscular system being strongly developed. The mouth-plates are small and remarkable 
for their simplicity and for the small amount of modification which the primitive 
constituent parts have undergone. The mouth-plates are distinctly seen to be adambu- 
lacral plates slightly altered in form and proportions; they are elongate and subtriangular, 
and extend from the margin of the actinostome to the interbrachial arc, occupying the 
whole of the breadth of the buccal ring (Sars’ term). The adoral ends are truncate, and 
the united pair have consequently a subhexagonal form, the median suture is wide and 
distinct, and more or less open outwardly. Each plate bears only two delicate spines, 
one close to the adoral margin and away from the median line of juncture, directed 
horizontally over the actinostome, the spines on two companion mouth-plates being parallel 
to one another. The other spine borne on the plate is a secondary or superficial mouth- 
spine, and is placed midway on the surface of the plate opposite the lateral angle. Both 
these spines are articulated on small tubercles; they are of nearly equal size, about 
1:75 mm. in length, and are encased in delicate membranous sheaths, crowded with pedi- 
cellarie. The adambulacral plate adjacent to the mouth-plates is very short; its breadth 
being greater than its length; in the next outward, these dimensions are about equal, and 
beyond this the length exceeds the breadth in increasing proportion. 
The madreporiform body is small, prominent, subtubercular, naked, with two or three 
very simple angulated furrows (in place of striations), and is situated close to the margin 
of the disk; it is not exactly in the median interradial line, but a little to one side, and 
consequently not immediately above the ‘‘ odontophore.” The latter plate is large, conspi- 
cuous externally, shield-shaped, and placed on the slope or bevel which intervenes between 
the plane of the abactinal surface and the extreme margin. 
Colour in alcohol, a bleached greyish white, with a faint pinkish shade over the ovarial 
regions, 
Localities.—Station 89, Between the Canary Islands and Cape Verde Islands. July 
23, 1873. Lat. 22° 18’ 0” N., long. 22° 2’ 0” W. Depth 2400 fathoms. Globigerina 
ooze. Bottom temperature 36°°6 Fahr.; surface temperature 73°°5 Fahr. 
Station 346. Between the coast of Africa and the Island of Ascension. April 6, 
1876. Lat. 2° 42’0”8., long. 14° 410” W. Depth 2350 fathoms. Globigerina ooze. 
Bottom temperature 34°°0 Fahr.; surface temperature 82°°7 Fahr. 
Remarks.—This species is remarkable in many respects, and very distinct from other 
forms. The small size of the disk in relation to the great length of the ray, the extent 
over which the plating is carried, the size of the plates and their unispinulate armature, 
the form of the adambulacral plates, the simplicity of their armature with the absence of 
the inner or furrow-margin spine, the corresponding simplicity of the mouth-plates, and 
finally the prominence of the odontophores and their unusual position, are a list of 
characters which do not occur in any of the other forms of Freyella or Brisinga, and 
cause this species to stand out with striking distinctness. 
