THE FAUNA OF THE ST. JOHN GROUP. 95 
the young of P. eteminicus, but disappears in the adult, is a permanent feature of some adults 
of P. acadicus (see page 103), another species occurring at St. John. 
Posterior margin—The furrow and fold are distinct, but exceedingly narrow, and 
notwithstanding the narrowness of the glabella and occipital ring the posterior margin is 
shorter in proportion to that portion of the shield (the glabella, ete.) than it is in the adult; 
the posterior margin was therefore in all respects less co :pletely developed than in the 
adult. The increase in the width, ete., of the posterior border in P. efeminicus is parallel to 
the change which occurs in Olenellus asaphoides Emmons (sp.) as described by S. W. Ford, of 
Troy, N.Y. in the Am. Jour. Sci, April, 1877. The embryonic forms of that species also 
exhibit a widening and strengthening of the posterior margin of the shield. 
The fixed cheek, on the contrary, at this early stage was of greater comparative size than 
in the later moults. The anterior end of the ocular lobe in place of being directed toward 
the summit of the dome of the glabella, as it is later in life, points more towards the anterior 
margin of the glabella. In very early stages of the organism the fixed cheek was of more 
importance relatively than other parts which become more prominent at a later period in 
the life of the trilobite. The relative importance of the cheek and glabella at successive 
stages is strikingly exemplified in the young of Conocoryphe Matthewi of the St. John group, 
and may also be traced in the embryonic forms of Olenellus asaphoides, cited above. 
The extreme narrowness of the glabella in this young individual of P. eteminicus, as 
well as its wide occipital ring and large fixed cheek, are parallelled by similar features in 
var. malicitus, described hereafter, which appears to have retained these juvenile features 
in its later stages of growth. 
10.2 MILLIMETRES (Fig. 11). At this stage an advance is made in some points toward 
the aspect of the adult form. 
Anterior margin.—The marginal fold is about twice as wide at the ends as in the middle. 
The flat area still connects in front of the glabella, but is proportionately narrower than 
in the 4.5 millimetre size, being about equal in width to the marginal folds. 
Glabella—tThere is little change in the position of the furrows, but there is a decided 
enlargement of the dome. 
Occipital ring.—The outlines remain, as in the smaller individual, and the spine about 
one-third from the back of the ring is distinct and directed backward. 
Posterior margin is somewhat wider and longer in proportion to the occipital ring and 
the eyelobe than in the 4.5 mm. size. The ocular measurement is six-thirteenths of the 
three measurements of the facial sutures (Nee table). 
Seulpture.—The raised parallel lines on the glabella are very distinct, but only a few 
could be traced on the anterior marginal fold; the cheeks are distinctly granulated, and a 
band of tubercles extends from the back of the occipital ring, along the axial line to the 
dome of the glabella. 
21.8 MILLIMETRES (near the size of Fig. 9).—At this stage there is a decided approach 
to the mature form in several features. 
Anterior margin.—The fold as in the last, but the flat area in front of the glabella is 
scarcely one-half of the width of the fold. 
Glabella —There is little change except that it is wider at the base. The fourth furrow 
