THE SILURIAN TRILOBITE LICHAS AUSTRALIS 
141 
Draws in a little at posterior end to accommodate itself to width of axial 
lobe of pygidium. Spines longer than pleurae proper; gradually tapering; 
directed slightly backwards and descending fairly steeply from the level 
of the pleural lobes, as in Lichas palmata Barrande. 
Pygidium sub-semi-circular, tuberculate. Axial lobe elevated; conspicu- 
ously narrower than axial lobe of thorax; occupies about three-quarters of 
length of pygidium. Width fairly even until posterior end where it fades 
out in a broad V-shape. Annulations cross lobe transversely, those nearer 
the thorax being strong but those at the posterior end difficult to trace. 
Tubercles follow' the annulations. Lateral lobes flat or lightly convex; each 
traversed by two prominent ribs, which make an angle of approximately 
45 degrees with the axial lobe. Above, betw'een, and below these ribs are 
faint ridges surmounted by tubercles. The pygidium has six short, stout 
spines, four being prolongations of the pleural ribs, and two projecting 
immediately below the axial lobe. The four lateral spines are directed 
backwards so as to make a more acute angle with the axial lobe than do 
the ribs. 
Measurements of complete carapace: Length (Including pygidial spines), 
30 mm.; width (including pleural spines), 26 mm. 
Apart from the structure of the cephalon, interesting and 
significant specializations in Lichas australis are noticeable 
in the tuberculate surface of the carapace, the spines which 
project from the lateral margins, and the elevation of the 
eyes on pedicels. The nature of the pleurae would allow a 
considerable degree of enrolment. All these characters have 
survival-value. The elevation of the eyes suggests a benthic 
habitat. The Lichadidae and the Odontopleuridae are 
the most specialized among the Opisthoparia. The high 
specialization, however, indicates a phylogerontic stage. 
Another noteworthy feature of the species under discussion 
is its possession of eleven thoracic segments. Typically, the 
genus has (as McCoy points out) ten segments. Barrande ’s 
Bohemian species also have eleven segments, which number 
appears to be characteristic of them ( ] ) . Among the trilobites, 
as well as in other groups, there is a strong Bohemian element 
present in the Victorian Silurian fauna. Barrande ’s 
Bohemian species Phacops fecundiis (in the slightly different 
form described by McCoy) is very abundant in the Victorian 
Yeringian. 
Specific affinities. — McCoy (3) compared the present 
species with Lichas haueri Barrande, which occurs in Stages 
F and G of Bohemia. Lichas australis is altogether a smaller 
form than L. haueri. In addition to the lobar differences 
between these species mentioned by McCoy, the nature of the 
eye-pedicels and the occurrence of three instead of two 
prominent tubercles in the sulcus at the base of the glabella 
appear to be established divergences. The thorax of L. haueri 
was not known to Barrande. The pygidium of L. australis is 
