94 G. F. MATTHEW ON ILLUSTRATIONS OF 
of the dash; “ +” indicates the direction (towards the head of the dagger) in which the 
test has been pushed by pressure. The specimen is supposed to be viewed with the 
anterior end upward. The figures in the columns of the table are proportional measure- 
ments, based on the length of the shield. 
MEASUREMENTS OF CEPHALIC SHIELDS. 













Suture. Axial Line. Transverse Diameter. 
Series ONE = Glabella. |, | Basal. | Middle. | Anterior. 
of ea aia Bg 2 || % _|S£ _| Distortion. 
SSL | SH! oF ||.28 aan | S2 |] a eia nina ee 
Growth. 2S|52/88|82||8hles/Es| 6 |ES|SES| Sum) 3/28! = 
GS OB aa lagio |28/se| 4 |= Sees) HS) 2182) 2 
ers) BA) eA) & | 2S SAAB ES | = 
ae le EN tat] 
4.5 millimetres.:07 |-50 |-21 |-18 ||-14 |-07 |-14 |-43 |-18 ||-24 |-29 |-36 |-29 |-29 |-43 | + 
10.2 us -08 |-44 |-28 |-17 |-16 |-09 |-13 |-50 |-09 |]-28 |*38 |-44 |-44 |-25 |:53 | + | slight. 
21.8 ss °12 |:47 |-24 |-19 ||-16 |-07 |:13 |-59 |-06 ||-30 |-41 |*41 |*44 |-32 |-65 | + | slight. 
22.4 “09 |+46 |-23 |-19 ||-14 |-09 |:13 |-57 |-06 ||-27 |-40 |-37 |-43 |:26 |-60 | 
24.4 “ ‘11 |-41 |-28 |-17 ||-17 |°08 |-11 |:58 |-07 ||-27 |-37 |:37 |-38 |-26 |-51 | + 
26.2 fs *07 |*46 |-24 |-21 ||-16 |-08 |-12 |-54 |-07 ||-28 |-41 |-40 |-46 |-23 |-67 | * slight. 
30.1 fs ‘11 |:48 |-28 |:20 ||:15 |-09 |-15 |-55 |-06 ||-31 |-47 |-42 |-48 |-29 |-64 | */ slight. 














4.5 MILLIMETRES (Fig. 12).—This form shows wide diversities from the adult in several 
respects :— 
Anterior margin.—The fold is nearly or quite uniform in width from end to end and does 
not show the regular expansion toward the extremity which is found to characterize adult 
and half-grown individuals. The flat area of the anterior margin goes entirely around the 
glabella, and is not interrupted in front of that part of the shield, as it is in the mature 
trilobite. The narrow part of the flat area where it passes around the front of the glabella 
is twice as wide as the corresponding part of the marginal fold. 
The glabella is remarkable for its narrowness, as compared with the same part of the 
shield in the adult. The want of volume is not confined to any one part of the glabella, 
but characterizes it throughout, and is a peculiarity which marks all the immature stages 
of the Saint John trilobites. This youthful character remains as a permanent feature in var. 
malicitus (described hereafter). 
Glabellar furrows.—Another point in which the young of P. eteminicus differs from-the 
adult is in the position of the glabellar furrows; ordinarily in P. efeminicus, a line connect- 
ing the two inner points of the fourth furrow is about half way from the front of the dome, 
but in this young individual it is only a third. 
The occipital ring differs widely in form from that of the adult: it is three times as 
wide in the middle as at the ends, and more than half as wide as long; there is a raised 
transverse lobe or elevation which occupies more than half of the length of the ring, and on 
the posterior third a small spine is set; this elevation disappears from the ring in the adult, 
but its position and former presence is indicated by a forward arching of the occipital fur- 
row in the middle half. This peculiarity of the lobe on the occipital ring which exists in 
ee eee Ste, à fn. 
