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. hdigenalis 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. Sweeil 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. 

 lafigenalis is very clear on (a) the greater number of eyelets on 

 each eye and the unvarying character of the eye; {h) the perpen- 

 dicular glabella sides; (c) distinctness of the lateral furrows of 

 the glabella on large specimens; and {d) the smallness of the 

 basal lol^es of the glabella. 



We have received a ver}^ well-preserved head from Mr. G. Sweet 

 (PI. xxxix.,fig. 2),whichhe informs us is the usual form of P.fecundus, 

 McCoy [Vnon Barr.). We believe it to be identical with the species 

 al)ove described, but still think that it is distinct from P.fecun- 

 diis, Barr. By this specimen we observe that the glabella sides are 

 perpendicular, the nodules of the intercalar}'- 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. AVales forms, and the perpen- 

 dicularity of the sides of the glabella is a feature not possessed 

 ]3y 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 simj)ly our united opinions based on the material we 

 ha-\'e been able to accumulate. 



IjOC. and Horizon. — Mansfield District, Victoria — % Upper Silu- 

 rian. Coll. — G. Sweet, Melbourne. 



