SMYNTHURUS. 103 



quite short, being *004" in breadth, and '005" in length. 

 The two following segments are of nearly equal size, 

 being each about •012" in length, and 002" in breadth. 



On the whole they are cylindrical, but their outline, 

 and especially that of the third, is somewhat knobby. 

 They bear a few scattered bristles, resembling those 

 on the head and body, and also a few smaller hairs 

 near their apices. The terminal portion of the an- 

 tenna resembles a necklace of beads welded together, 

 and gradually diminishes in size at the tip, though, 

 for the greater part of its length, it has a diameter 

 across the beads of "OOIS". At each projection is a 

 whorl of small hairs, and at the apex are a few rod-like 

 hairs, resembling those found on the antenna of so 

 many insects and Crustacea, and which are doubtless 

 organs of sensation, though I was unable, from their 

 minute size, to ascertain their structure in a satisfactory 

 manner. 



The labrum is a simple, entire, quadrate, horny lobe, 

 somewhat broader at the base than at the apex, with 

 a few scattered hairs, and a row of teeth at a little 

 distance from the free border, those on each side 

 being parallel, and opposite to those of the other 

 side; so that they all point inwards. The mandi- 

 bles are rather small, and differ somewhat from one 

 another, though they agree in general outline. The 

 basal part is long and somewhat cylindrical, with 

 a large gaping orifice, through which the muscles pass 

 into the head. The whole organ is about '03" in 

 length ; at a distance of about "02" from the base is a 

 raised molar surface which is covered with minute, 

 rather blunt teeth, and, in conjunction with the cor- 

 responding portion of the opposite mandible, evidently 

 serves the function of mastication. The terminal 

 incisive portion is dissimilar in the two mandibles ; the 

 one has six teeth, the other only three, which fit into 

 the intervals of the first. This part of the mandible 

 diminishes rapidly in thickness towards the tip ; the 

 dorsal fine, however, is continued throughout in the 



