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ribs coloured more distinctly and transversely dotted with darker red. Radii rather broad, not 
very distinct, however, in the specimens with correded surface; coloured white or faintly reddish 
in the specimens with ribbed surface, and being transversely striated in these specimens, more 
distinctly so in the upper half. Orifice small, elongately pentagonal, nearly entire, certainly 
not toothed; the recurved tips of the terga occupy the carinal angle of the orifice in a very 
peculiar way. ‘Together with the extreme narrowness of the carino-lateral compartments, 
causing the radii of these valves and those of the rostro-lateral compartments nearly to touch 
each another, the characteristic appearance of the tips of the terga will always make it easy to 
recognize this species. % 
Parietes (Pl. XXI, fig. 7, a, 6 and c) solid, no pores, but with well-developed longitu- 
dinal ribs, forming so many septa, which are denticulate in their basal parts. The sheath is 
transversely ribbed. The radii of the carino-lateral and rostro-lateral compartments nearly touch 
each another, owing to the extreme narrowness of the carino-lateral compartment (PI. XXI, 
fig. 5). The sutural edges are coarsely ribbed transversely. The basis is thin, attached firmly 
to the surface of the calcareous plate and has no pores; it adheres very firmly to the walls 
of the valve and is perfectly flat — not cup-shaped, and not imbedded in the coral at all. Its 
interior surface shows delicate ridges radiating from the centre. 
Greatest diameter of the basis of one of the larger specimens about 7 mm. 
Scutum (Pl. XXI, fig. 6, @ and c) the lines of growth are very distinct and are beset 
with a number of small points making them look as if crenated; occludent margin distinctly and 
more or less irregularly toothed; articular ridge not very prominent and extending down from 
the apex to about two thirds of the length of the tergal margin; adductor ridge indistinct; 
cavity for the lateral depressor muscle well-developed; along the tergal margin the surface of 
the valve is uplifted, the growth-ridges being here very distinctly crenated or toothed. 
Tergum (Pl. XXI, fig. 6, 6 and d@): apex distinctly produced, beaked, carinal margin 
convex, scutal margin strongly hollowed out, basal margin sinuous. Ridges of growth not very 
distinct, external surface almost flat, without a longitudinal furrow; spur situated quite close to 
the scutal angle of the valve, its extremity being almost confluent with that angle, not very 
short, and not quite half as broad as the valve itself. Crests for the depressor muscles indicated, 
but not very prominent. Articular ridge distinct only in the uppermost part of the valve. 
Tergum extremely brittle — it is difficult to prepare a really faultless specimen of it. 
With regard to the structure of the animal’s body the following may be of interest: 
Mouth. Labrum (Pl. XXI, fig. 8): The outlines of the lateral parts of the labrum 
together make an angle; the notch is deep and not very wide at the entrance. Three 
well-developed and sharp teeth on each side of notch. 
Palpi elongate, nearly oval, not club-shaped. Hairs along upper margin form a dense 
and regular row. Those on outer surface long, and placed in rows which make angles with 
the inferior margin near distal extremity. On the inner surface a longitudinal series of shorter 
hairs is disposed and this runs parallel to the upper margin, the hairs overlapping the edge 
of the labrum when the palpus is directed downwards. Extremely delicate ciliae are disposed 
along part of inferior margin and rounded distal margin. 
83 
