434 MR. LUBBOCK ON THE THYSANURA. 
figs. 1, 2, 3, 4), though they agree in general outline. The basal part is long and some- 
what 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 corresponding 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 inter- 
vals of the first. This part of the mandible diminishes rapidly in thickness towards the 
tip; the dorsal line, however, is continued throughout in the same direction, though 
with three gentle curves resembling in direction, though less abrupt than, those of a bow 
or a reversed S. The front line of the mandible, on the contrary, makes a sudden change 
of direction at the beginning of the molar portion, so that the terminal part of the 
mandible seems to lie in a different plane from that of its basal part. 
The maxillae (PI. XLV. figs. 5, 6) are a little shorter than the mandibles. The width 
varies, being smallest towards the upper end, and greatest towards the middle. The 
upper extremity is terminated by a somewhat complicated system of teeth. First, there 
three strong curved teeth, the outer one being the largest, and the 
the 
smallest. In addition to these are two lamellae, whose inner edges are beset with a row 
of minute, sharp projections. Lastly, there is a large central, somewhat fan- shaped lobe, 
the central part of which bears some fine hairs on the margin. All these parts appear to 
have some power of independent movement. The body of the maxillae is strengthened 
by a chitinous framework ; down each side runs a strong rib, while the two are connected 
at the centre by a transverse piece, which is also continued on the inner side a little 
way beyond the rib, and curves at the same time so as partly to surround the softer 
parts. The two lateral ribs converge to meet one another at the base as at the apex. 
At the former, however, they enclose a space which has the form of an acute triangle, 
while at the basal end they curve round to meet one another. At the base the chitine is 
rounded off on the outer side, but is produced into a sharp point on the inner edge. 
The palpi (PL XLV. fig. 8) are short, one-jointed, rounded but not tapering at the 
free end, and with two longish setae and one or two minute hairs, none of them, however, 
attached at the apex. 
The second pair of maxillae are membranous and delicate. Their form (PI- XL v. 
fig. 9) is somewhat difficult to describe. At the extremity are two teeth of unequal size ; 
on the basal side of these are three more or less projecting lobes ; and then follow a 
number of small teeth, which end at a point where the two maxillae converge toward 
the middle line so as to touch one another. 
The under lip is stronger, and consists of two more or less quadrate lobes. 
The feet of Smynthurus are very peculiar, and differ in the different species. Nicolet 
has given two figures of a foot, seen from different sides ; but neither of them agrees 
altogether with any of those examined by me. In my specimens the tarsus was very 
short, and bore two peculiar appendages. On the outer side was an elliptic, elongated 
claw, transparent above, terminating in a spine, and bearing also one large tooth and 
three smaller ones on its underside. On the underside of the tarsus is a second claw, 
s 
