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Surface of the shell granulated (Pl. X XVII, fig. 1), with indistinct furrows which extend 
irregularly over the lower, wider and cylindrical part of the shell, and which radiate from the 
orifice in the upper, slightly narrower part. In consequence, the orifice is surrounded by a circle 
of small areas, which are separated from each other by the furrows and which are of a 
lighter colour, the remaining part of the shell being of a darker, greenish-brown colour. The 
orifice is elongately-oval, not quite three times as long as broad, small; its carinal extremity 
rounded, the rostral one being pointed. ; 
Shell thick, having small and not very distinct pores at irregular distances in the outer 
layers and having the internal surface strengthened by vertical septa. Sheath not large, 
extending only to the point where the conical and vertical parts of the compartments meet. 
Basal part of shell only very superficially embedded in the surface of the coral in one specimen, 
and much more distinctly, especially at the carinal extremity of the shell, in the other. 
Size of the largest specimen 10 mm. in its longest diameter, of ‘the smallest 7 mm. 
The scutum and tergum (Pl. XXVII, fig. 2) are closely united, and even calcified 
together in the specimen I dissected. The line of junction between the two makes a not very sharp 
angle with the strongly curved occludent margin of the scutum. This valve is not very elongate, 
being slightly more than twice as long as the height near the line of junction. The scutum 
narrows towards the rostral end, where the basal and occludent margins meet in a somewhat 
produced angle. Along the occludent margin there is a strong ridge or ledge which bends inwards. 
The basal margin is concave, the adductor ridge developed into a rather broad plate, which 
projects considerably below the basal margin. : 
The tergum is relatively large, its surface being hardly smaller than that of the 
scutum; spur well-developed, with the extremity bluntly pointed. Crests for the attachment of 
the tergal depressor muscles distinct and projecting beyond the basal margin. 
The study of the structure of the animal contained within the shell has yielded the 
following results: 
Mouth. Labrum deeply and widely notched; a pair of very small triangular teeth, 
and numerous short and stiff hairs on both sides of the notch. Palpi-.stout, short and broad, 
with the lower margin straight and the upper rounded; along the lower margin shorter 
hairs are observable, longer ones at the tip, and very long and strongly curved hairs at and 
near the upper margin; the hairs at the tip are so densely disposed as to form a distinct tuft. 
Mandible with five teeth, and quite a rudimentary inferior angle terminating in a 
group of very small, pointed teeth. The first tooth is relatively short and single, the second 
and third teeth are distinctly double, teeth four and five standing close together, short, broad 
and blunt. Hairs along the posterior margin of the inferior angle not very numerous, standing 
close together and being relatively strong. ; 
Maxilla short, with the edge rather long and perfectly straight and with the upper 
and lower margins nearly parallel. Nine spines are seen along the edge; only the two 
superior ones are broader and slightly longer than the others; a very rudimentary notch is 
observed under the two superior spines; between the spines a number of delicate hairs 
are seen. 
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