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The terg urn (PI. XXVII, fig. ïiè) 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 resembline 

 in many respects the corresponding parts of Darwin's var. (i). 



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 (PI. 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. 



Pal pi 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 doublé row ot 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 (PI. 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 doublé 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. 



Maxi 11a (PI. 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 nd and 4" 1 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 

 1 ong and slender. 



Outer maxillae (PI. 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. 



Cirri. Cirri 1 to 3 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 tracé of teeth on inner face of 

 lower segments. 



13S 



