THE FAUNA OF THE ST. JOHN GROUP. 105 
MEASUREMENT OF CEPHALIC SHIELD. 















Suture. Axial Diameter. Transverse Diameters. 
Glabella. Basal. Middle. | Anterior. 
8 : Bales Sa istorti 
Length. Gees [2e | Of 8 | = 7 Distortion. 
£È ge or TB é | Se og|3. ad B/isa| 2 
nD oO ao = Er © = Bea | = 
ay Al ||) sl) 8 
7:7 millimetres.|°08 |:27 -17 |:08 |-10 |*42 |-15 33 42 |-27 |-58 | — slight. 
| 
8:3 i 09 |-58 17 ||:16 |-08 |-11 |-54 31 |-39 |°37 |-39 65 | + | 
09 8 « 09 |-53 |-21 |-18 ||-16 |-09 |-12 |-53 |.09 ||-30 |-47 50! fem | + 
12°8 ge *09 |-50 |-20 |°22 ||15 |°10 |-10 |-55 |-07 ||°35 |-46 |°40 |-45 |°20 |:62 | + 
| 
12°8 ch 09 |:45 |°25 |:22 ||-15 |:10 |:13 |-52 |-07 ||-37 |-45 |-42 |-48 |-25 |-60 | — | 
| 
15°4 °08 |°46 |:23 |-21 ||-14 |-08 |-14 |:56 |-06 ||-33 |-42 |-44 |-50 |-25 |-66 | — 














Marginal Fold—In the first stage observed (fig. 18), there was a space in front of the 
glabella separating that part of the shield from the marginal fold; at this period the space 
in front of the glabella was equal in width to the marginal fold, but at the 10.9 mm. it is 
obliterated by the meeting of fold and glabella. 
Glabella—The glabella dome shows the usual lateral enlargement, and the fourth 
furrow the gradual retrocession from the front of the dome; in the youngest stage observed 
it is half-way from the front, then in later stages the fourth furrow is found to be about 
three-fifths from the front as in P. eteminicus, and finally at the largest stage (fig. 17) it is 
three quarters from the front of the dome. 
The occipital ring as in P. eteminicus and its allies becomes gradually reduced in width, 
and the posterior side of the shield lengthened as in those forms. 
The fixed cheek changes its form during growth, increasing in width and decreasing 
in length. The increase of the width of the fixed cheek is more decided and regular in 
this species than in P. eteminicus and its related forms, and in this respect reminds one more 
forcibly of the gradual outward arching during growth of the eye-lobe in Olenellus asa- 
phoides. The gradual modification of the shield of P. acadicus is evidently parallel to that 
which occurs under similar conditions in P. efeminicus and its allies. 
Sculpture—The youngest shield of P. acadicus was obtained at Hanford Brook in 
St. Martin’s, and like most of the tests from that locality is very thin: the cheeks are 
wrinkled by pressure, and the granulations on the surface are very delicate ; a lens of 1 in. 
focus is sufficiently powerful to resolve the markings. The head is remarkable for the 
unusually great expansion of the anterior margin, and there are one or two raised lines 
discernible on the front of the fold. At the 12.8 mm. stage (fig. 16) the granulations on 
the test of this species become visible to the naked eye, and in the mature trilobite are 
very distinct. 
PARADOXIDES LAMELLATUS (Hartt). 
Professor C. F. Hartt describes this “as a small species distinguished from several 
others found with it by the presence of a number of sharp perpendicular laminæ on the 
Sec, IV.,1882. 14 
