THE FAUNA OF THE ST. JOHN GROUP. 93 
is deeply impressed in the outer quarter of its length; the middle half is more lightly 
impressed, and is convex forward. 
The posterior margin is arched vertically in the middle, and also arched backward in 
the outer half. The marginal fold is narrow, is flattened and widens a little in the outer 
half, and slopes gradually to the posterior furrow. The furrow is about fhree times as wide 
as the fold, is broadly rounded in the bottom, and depressed at both ends, especially the 
outer. 
The fixed cheek is broad, particularly in the posterior third, and a slight depression runs 
lengthwise across it; the posterior end is elevated next the glabella and the bounding fur- 
rows of the cheek are shallow, but distinctly defined. The ocular lobe has a full parabolic 
eurve of which the chord is more than twice as long as the height of the curve ; the posterior 
end is elevated into a tubercle-like lobe which overhangs the posterior marginal furrow. 
Sculpture—The anterior marginal fold is traversed by very fine parallel raised lines, 
which at intervals anastomose, or die out on the surface of the test. There is a good deal of 
variation in the number and fineness of these lines, which are more widely set on the inner 
two-thirds than on the outer edge of the marginal fold; there are from eight to twelve of 
these lines toward the outer end of the fold; in some cases there are about four widely set 
lines on the inner three-fifths, and about six closely set lines on the outer two-fifths of the 
marginal fold. The front half of the dome of the glabella is omamented with irregularly paral- 
lel, occasionally forking, concentric, raised lines, similar to those of the anterior marginal 
fold, but more distinct ; these lines are most widely set on the front slope of the dome where 
there are about 4 or 4} in the space of one millimetre. There is a band of small tubercles 
extending along the axial line of the shield from the posterior edge of the occipital ring to 
the dome of the glabella; these tubercles are most distinct on the occipital ring and can 
scarcely be resolved by the eye along the rest of the band, but are clearly discerned with a 
moderate magnifier. A similar band of smaller tubercles extends along the posterior furrow 
and passes thence into the inter-ocular furrow, along which it extends as far as the anterior 
end of the ocular lobe. The rest of the shield is covered with minute granulations, visible 
with a lens of one inch focus, which blend with the bands of tubercles above described. 
Dimensions.—The largest shield observed was about an inch and quarter long and an 
inch and a half wide. 
Locality —This species is of frequent occurrence in the slates of Division 1c. in Portland, 
and has also been found at Radcliffe’s stream, Simonds, St. John county. 
Name.—Derived from that of a tribe of Acadian aborigines—the Etchemins. 
Growth and Development of the, Young. 
ser | le 
meer Lilo 
Five or six stages in the growth of this species were observed, in which a very consi- 
derable change takes place from the young to the adult form. In order to make these 
changes during growth more clearly appreciable, the writer has appended a table of mea- 
surement of several heads obtained near St. John, and has noted in the margin the amount 
and direction of the distortion of the test, to explain some anomalous measurements which 
appear in the table. The following marks are used: “o,” indicates that the natural form 
has been preserved ; “+,” indicates that the specimen has been flattened, but not distorted 
laterally ; ““—” indicates that the specimen has been contracted transverse to the direction 
