58 Mr. R. I. Pocock on Isometrus americanus (Linn.). 
smooth suleus; between this sulcus and the keels on each side 
are a few granules disposed in two masses ; anterior portion 
of cephalothorax between the anterior keels and the lateral 
eyes and the posterior portion at the sides sparsely granular ; 
the lateral eyes about equally distant from each other ; 
median eyes separated by a space which is about equal to the 
diameter of each eye. 
Tergites more or less granular, the first marked in its pos- 
terior half by a transverse series of granules, which, almost 
marginal in the middle, curves forwards at the sides; the 
third with a short, median, longitudinal series of granules in 
its hinder third and on each side a conspicuous, slightly 
curved, transverse band, composed of many close-set granules, 
which does not reach the lateral margin of the tergite; the 
second in appearance midway between the first and the third ; 
the fourth, fifth, and sixth resembling the third, but having 
the bands of granules more pronounced; the seventh marked 
in front with a median, short, granular prominence and on 
each side two granular keels, which, curving towards each 
other in front, unite some distance in front of the anterior 
margin of the tergite. 
Sternites in part very finely and sparsely granular, dull- 
coloured, shining and smooth only behind and in the middle 
line. The fifth marked with four finely granular keels—two 
median, parallel, longer ; two lateral, posteriorly converging, 
shorter. 
Stigmata slit-like. 
Tail robust, nearly parallel-sided, the fifth segment only 
very slightly wider than the first, about five and a half times 
the length of the cephalothorax ; intercarinal spaces very 
feebly granular; upper surface scarcely at all hollowed; the 
fourth segment alone bearing in front a conspicuous depres- 
sion; the keels bluntly and almost evenly denticulated 
throughout, the terminal granule of the superior keels of the 
second, third, and fourth being alone a little more prominent 
than the rest. The first segment furnished with ten complete 
keels; the second, third, and fourth with eight, the median 
lateral keel being wholly absent on the third and fourth and 
represented by merely a few granules on the posterior half of 
the second; in the fifth the granules of the inferior surface 
show a tendency to arrange themselves in a definite series on 
each side of and parallel to the median granular keel; upper 
surface of this segment nearly flat, bearing only a very shal- 
low median sulcus. 
Vesicle feebly and bluntly granular below, with a more 
conspicuous granule immediately beneath the aculeus. 
