PLATE XXII. 
OLENELLUS) HOWELED << 0c cccuiscoc'so ne 3-00 cose nse enarisren ne sees eameenice rinrin= so =scee/o=5= 
Fig. 1. Outline of the smallest head of this species discovered. Natural size. 
2. Head showing the anterior position of the genal spines, 9 9, and the angles of the 
posterior margin, «x, extravagantly developed. The difference in the length of 
the ocular ridges of the right and left side is also very marked. Natural size. 
. The smallest individual in which the posterior course of the facial suture was 
observed. The outline of the head is much like that of fig. 1. Natural size. 
4, Form intermediate in contour of head, between figs.2 and3. gg, Genal angles 
and spines; #2, angles of the posterior margin. Natural size. 
. The eyes in this specimen are no longer pedunculated or united to the glabella by 
an ocular ridge, and the genal angles are more posterior. The course of the 
facial suture in front of the eye is also seen for the first time. Natural size. 
6. Example in which the genal angles are in the same position as in the adult indi- 
vidual in species of the genus. The eyes are more embryonic in character than 
in the preceding example. Natural size. 
7, Narrow form, with the eyes of the adult type, and having the genal angles carried 
forward, as in the younger individuals, 1, 3,5. Natural size. 
8, Broader and more common form showing the same peculiarities as fig. 7. Natural 
size. 
9. The right and left sides are irregularly developed, the genal spine on the left side 
being more anterior in position. The course of the facial suture is traced in 
accordance with its position, as observed in fig. 6. Natural size. 
iJ) 
ao 
QOLENELLUS ASAPHOIDES Emmons. ...--.-.-----.----- -----+ ---+------- seb ode Shoo ose aaa DSIOD 
Fig. 10. Embryonic form, showing the circular outline, the genal spines in close proximity 
to the facial suture, and the interocular spines. Enlarged to 3.5 diameters. 
(After Ford.) 
11. Another phase of the development of this species, succeeding, with probably in- 
termediate forms, fig. 10. The posterior of the genal spines, gg, and the sutures 
cutting the posterior margin at the angles, xx, are comparable to the same in fig. 3. 
Enlarged to five diameters. (After Ford.) 
12. Normal adult type of head of this species, enlarged totwo diameters. (After Ford.) 
OLENELLUS GILBERTI.. ..-.------ --- 022 22 o ne ene en ee eee eee nee rene ane te eees cone raceee 
Fig. 13. Small head, natural size, for comparison with figs. 2, 3, etc., of its associate species, 
O. Howelli. A large head is figured on plate ix, fig. 16. 
14. Narrow form of head, that shows the angles in the posterior margin, «, slightly 
developed. Natural size. (After White.) 
PARADOXIDES KJERULFI Linnarsson...--. .----- --20 2-22 22 enn cece cones cone cee ene eee e enee 
Fig. 15. Outline of head showing the position of the genal angles and angles of the pos- 
terior margin, #7, with the interocular spine; also the ocular ridge (a) uniting 
the glabella and eyes. (After Linnarsson.) 
OLENELLUS HOWELLI .... .... ---- 222 22 ee ne ee ee ne ee eee ne ne ee ne ee ce en ce ete ne ee ee eee eens 
16. Outline of hypostoma found associated with this species. Enlarged to three diam- 
eters. 
17. Free cheek found detached from the fixed cheek. The direction of the suture in 
front of the eye is well defined, s; its direction posteriorly may be along the line 
of fracture, 0 0, but it is impossible to satisfactorily determine it. If, as in fig. 6, 
it would follow the dotted line, o . 
