1869. | DR. A. MACALISTER ON GYROPUS DICOTYLIS. 421 
concave, and the posterior convex, ie apex of the lobe being directed 
forwards and outwards. This appearance is similar to the arrange- 
ment of these lobes in G. ovalis of the Guinea-pig. Frontal margin 
convex, obtuse, fringed by a few hairs ; eye very small, inconspicuous, 
situated in front of the temporal sinus on the upper surface of a 
Gyropus dicotylis (magnified). 
small eminence, and guarded by a few hairs. Occipital margin con- 
vex on either side, slightly concave in the centre, but not nearly so 
much as in G, ovalis. The antennz have their basal joints cylin- 
drical, large, the second short and rounded, the third club-shaped, 
the fourth and last is large and dilated, bent upwards and backwards ; 
these joints are well defined, and each one begins extremely narrow. 
In G. ovalis the last joint is securiform ; in the present species it is 
more club-shaped. ‘The maxillary palpi are four-jointed, each joint 
being more slender than its precessor, the terminal Seamcnt being 
the smallest, and the third the longest. 
The neck is one-third the breadth of the head (one-half in G. ovalis). 
Prothorax hexagonal, flattened, wider transversely than antero-pos- 
teriorly, smaller than the head ; this segment is longer than the head 
in G. longicollis of the Agouti, but it is equal to it in G. hispidus (the 
parasite of the Three-toed Sloth). There is no trace of the transverse 
depressed line on the prothorax, which is characteristic of G. ovalis. 
Sternum slightly prominent. The union between the prothorax and | 
the combined meso- and metathorax is of the same size as the neck. 
This compound segment is quadrilateral, wider behind than in front, 
and bearing the two posterior pair of legs, between which opens, 
on each side, a spiracle. It is once and a half the length of the 
prothorax, and very slightly wider. The first pair of limbs are °05” 
long, with a single incurved unguis. The tibia is armed at the 
junction of its middle and lower third with a prominent tooth, which 
Proc. Zoou. Soc.—!869, No. XXVIII. 
