What i.i the Olenellus Fauna? — Mattheiv. 399 
cott, belongs to the Olenellus fauna, being associated with the 
original Olenellus of Hall. 
There still remains another group of olenellid trilobites 
represented by the type species and remarkable for their tel- 
son-like pygidia. All these have the enlarged Paradoxides- 
like front to the glabella. Are they to be referred to Holmia 
kjeridji branch of the olenellid stock or to an ancestral type 
unknown? We think to the latter. This seems to have been 
a branch which has left widespread evidences of its distribu- 
tion, having been found in Scotland and both in the east and 
west of America, but nowhere has it been seen beneath the 
Paradoicides beds. It is a branch of the olenellid stock, whose 
position relative to Paradoxides has yet to be determined. 
That it is a highly developed branch of the olenellids ma}^ be 
inferred from its glabella and peculiar pygidium, and we there- 
fore think it is not the oldest. 
From the study of the youngest of Paradoxides we judge 
that the enlargement of the front lobes of the glabella in this 
genus and in Olenellus is not a i^rimitive character. It is not 
analogous to the enlarged front of the axial lobe of the 
cephalic shield seen in the protaspis and early larval stage of 
many trilobites, for we find that in the larval condition of Par- 
adoxides these lobes are shorter than in the adult forms. 
Notwithstanding the difference in the facial suture we feel 
that Paradoxides and Olenellus are not far removed from each 
other, and that the enlarged front of the glabella in both points 
to a similar development in the two genera in this respect. 
Nor can we suppose that the spine-like pygidium is a protas- 
pid character in Olenellus (sensu stricto) ; we would rather 
expect to find that in the early stages of growth this branch 
of the olenellids would be found to have a normal pygidium 
like that of the other two branches of the stock. 
Peach, who has written on the question of the relations of 
the different forms of the olenellid stock to each other,* looks 
upon H. kjervlfl as the initial form of the olenellids. but we 
must remember that this form is in the beds which in Sweden 
lie immediately beneath the Paradoxides beds. A thickness 
*Addition to the Fauna of the Olenelbjs Zone of the Northwest High- 
lands, by B. N. Peach., Esq., Quart. Jour. Geol. Soc., Nov., 1894, p. 
671. 
