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The tergum (Pl. XXVII, fig. 114) is thin and very brittle; its beak is not produced, 
its scutal margin nearly straight, its spur is about half the width of the valve. The basal end 
of the spur is rounded off, the basal margin of the tergum slightly hollowed out. The whole 
valve is about two-thirds of the width of the scutum, this valve like the scutum resembling 
in many respects the corresponding parts of Darwin’s var. (1). 
Darwin did not give a description of the mouth and cirri of this genus. He pointed out 
in the description of the genus only that in the characters derived from these parts there are no 
generic differences between the genera Pyrgoma and Creusza. I think it of some importance to 
give here a short description of these parts in the present variety, so far as I have been able 
to study them. 
Mouth. Labrum (Pl. XXVII, fig. 12). Lateral margins on both sides of notch make 
an angle; notch rather wide at entrance and not very deep. There are found 3 to 4 teeth on 
either side of the notch, one of these on either side being much smaller. No hairs are obser- 
vable on the margins of the notch or along the edge of the labrum. 
Palpi oval, the upper and lower margins nearly parallel, the free extremity broadly 
rounded off. Delicate hairs are disposed along the lower margin; the stronger hairs along the upper 
margin are developed only on the distal part of that margin. The outer surface is furnished 
with a group of longer spines or spine-like hairs, which also occupy only, the distal extremity 
and which meet downwards with a double row of such spines, making an angle with the 
lower margin. The inner surface is covered with numerous shorter and curled hairs, part of 
which fall over the free edge of the labrum so long as the palpus is not lifted up. 
Mandible (Pl. XXVII, fig. 13). Distance between extremities of teeth 1 and 2 greater 
than that between teeth 2 and 3. One and two of about the same size, 3 somewhat shorter; 
2 and 3 are indistinctly double at the extremity. Tooth 4 represented by a blunt triangular 
knob, larger at the mandible of the one side than at the other. Tooth 5 and inferior angle 
form together a small truncated projection. Row of hairs along inferior margin rather elongate. 
Maxilla (Pl. XXVII, fig. 14). Edge straight, making a rectangle with the inferior 
margin. Spines of the upper and lower pairs of about the same size. Between these two pairs, 
five intermediate ones are disposed, the 2™4 and 4‘ of which are slightly longer than the other 
three. There is no notch behind the upper pair, but all. the spines are disposed at small 
distances from each other. Among the spines numerous long hairs are inserted. Apodeme 
long and slender. 
Outer maxillae (Pl. XXVII, fig. 15). Outer lobe broken off, lost; inner lobe somewhat 
elongate, covered over inner surface with several rows of partly feathered hairs. These stand 
off horizontally or are directed towards the basal part of the maxilla. 
Cir." Cirn 1013 lost. 
Cirrus 4 has slightly unequal rami of 13 to 14 and 14 to 15 segments. The middle 
segments are less than four times as long as broad, and bear 2 pairs of spines on their inner 
faces. On the outer side, each segment bears a few hairs at the extremity, one of which 
is rather long, nearly as long as the segment itself. No trace of teeth on inner face of 
lower segments. 
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