500 
SILURIAN TRILOBITES, 
separation. It differs from P. Crossleii by the much greater 
length of its genal lobes, which are conspicuously large. With 
our P. latigenalis it agrees in having a great length of cheek 
between the posterior angle of the eye and the genal angle. 
The glabella of this species appears to have been granulated in 
the manner common to the genus, but our specimens are all decorti- 
cated, and the indications of granulation are observable on the 
moulds only. 
The neck ring of P. Sweeti is proportionately wider than either 
of the N.S. Wales species, which would indicate a wider propor- 
tionate axis. That it is quite distinct from P. Crossleii and P. 
latigenalis is very clear on (a) the greater number of eyelets on 
each eye and the unvarying character of the eye; (6) the perpen- 
dicular glabella sides; (c) distinctness of the lateral furrows of 
the glabella on large specimens; and (d) the smallness of the 
basal lobes of the glabella. 
We have received a very well-preserved head from Mr. G. Sweet 
(PL xxxix.jfig. 2),whichhe informs us is the usual form of P.fecundus, 
McCoy i^.non Barr.). We believe it to be identical with the species 
above described, but still think that it is distinct from P.fecun- 
dus, Barr. By this specimen we observe that the glabella sides are 
perpendicular, the nodules of the intercahuy ring lie right in the 
path of the axial furrows, and that the lobes between the inter- 
calary and basal glabella furrows are very small. All these 
features separate it from the N.S. Wales forms, and the perpen- 
dicularity of the sides of the glabella is a feature not possessed 
by P. fecundus, Barr. The whole form of the glabella approaches 
as near to the quadrate as the pentagonal form. 
It is not for us to dogmatise on this point, nor to adversely 
criticise the work of so accurate an observer as Sir F. McCoy. 
The above is simply our united opinions based on the material we 
have been able to accumulate. 
Loc. and Horizon. — Mansfield District, Victoria — ? Upper Silu- 
rian. Coll. — G. Sweet, Melbourne. 
