THE FAUNA OF THE ST. JOHN GROUP. 92 
I have described thus fully the gradual change in the cephalic shield of P. eteminicus 
during its growth because of the interest that attaches to any feature of structure bearing 
on the origin and development of species, especially of such remote antiquity. 
In the changing form of the glabella and other parts of the buckler, there are 
features which remind one of the changes observed by Barrande, in the growth and 
development of Sao hirsuta, a trilobite of Bohemia. To the earliest stages of that species 
the Acadian beds have as yet furnished no parallel. But of that wherein the central lobe of 
the cephalic shield begins to be segmented, there is an indication in the earliest known 
form of P. eteminicus in the preponderance of the occipital ring, which projects behind the 
posterior margin, has a thin and leaf-like aspect behind, and possesses much greater com- 
parative width than at the later stages of growith. The weakness of the posterior margin, 
also, in the early stages of our species, indicates its immaturity and recent appearance. 
The gradual development of the anterior end of the glabella in Sao, finds its counterpart 
in P. eteminicus in the retreat of the furrows from the front of the glabella during growth, 
and the gradual absorption of the flat area of the anterior margin. But in the enlargement 
of the front, or dome in P. eteminicus, a characteristic feature of the genus Paradoxides 
becomes prominent, which is not to be looked for in Sao, and which does not appear in the 
figures of S. hirsuta. 
It is not impossible that there may also be some meaning in the gradual retreat of the 
eyelobe from the posterior margin by the widening of this part, and by the less rapid growth 
of this lobe than of other parts as the animal continued to increase in size. This, it appears 
to the writer, may be taken to indicate that the forms with continuous eye-lobes are a more 
primitive type than the Paradoxides with contracted eyes. Looked at from this point of 
view the var. quacoensis (described hereafter) is the most advanced type of the genus yet 
found in the St. John basin. 
VARIETIES OR SUB-SPECIES OF P. ETEMINICUS. 
The form of trilobite described in the preceding pagès is the central one of a number 
showing various points of diversity, but possessing in common one distinguishing character 
which separates them from the two succeeding species, viz: fine concentric raised lines on 
the front of the glabella. These points of diversity are in some cases probably of specific 
value but, for the present and till fuller knowledge is obtained, it seems desirable to keep 
together under one specific head the various forms having the raised lines on the glabella. 
The forms thus characterized, omitting the central type already described, may be dealt with 
in succession, beginning with those that have the shortest axial diameter. 
Var. SURICOIDES (Figs 4-6). 
This variety is not so common as P. efeminicus, but appears to have attained a larger 
size. It differs from that form in the following respects :— 
Glabella.—The length and breadth are nearly equal. The dome of the glabella is larger, 
higher and oblately orbicular. The glabellar furrows are more heavily impressed : the fourth 
furrow is three-fifths (the length of the dome) from the front of the dome. 
The occipital ring is rounded along the posterior margin in a more regular curve than 
Sec. IV., 1882. 13 
