RHIZODONTIDiE. 
347 
the clavicle of each side is marked externally with fainter, 
though almost equally coarse, reticulations. The last- 
named hone in each case is imperfect superiorly, hut the 
lower expanded portion (PI. XII. fig. 6) is relatively 
longer and narrower than the corresponding part of the 
clavicle in H. hibberti (PI. XII. fig. 3). Xo traces of the 
pectoral fins are preserved, and most of the scales are 
seen only from the inner side. Some scale-fragments 
(PI. XII. fig. 8), however, show that “the exposed area 
of the external surface is marked with short, interrupted, 
wavy, reticulating ridges, whose direction is mainly 
parallel with the posterior border of the scale; while in 
the interval between these, more delicate ridges are seen 
radiating from the centre ” (Traquair). Enniskillen Coll . 
P. 363. Portion of dentary with teeth, associated with imperfect 
scales. Purchased , 1881, 
P. 3320. Portion of dentary with teeth ; Burdiehouse. 
Enniskillen Coll. 
P. 3321. Left principal jugular plate and operculum, associated with 
the infraclavicle of the right side. The operculum, with 
its characteristic ornamentation, is shown, of the natural 
size, in PI. XII. fig. 5, and the infraclavicle, from the 
inner aspect, in fig. 7. As remarked by Traquair, the 
last-named bone has a relatively less antero-posterior 
measurement than the corresponding element in P. hibberti. 
Enniskillen Coll. 
P. 3322-a. Operculum associated with left infraclavicle and other 
fragments; also two imperfect detached opercula. 
Enniskillen Coll. 
36911-12. Operculum and (?) suboperculum. Purchased , 1863. 
47718. One of the principal jugular plates, in counterpart; Calcife- 
rous Sandstone, Burdiehouse, near Edinburgh. 
Presented by Dr. Lauder Lindsay , 1876. 
21223, 21421. Two small scales, inner aspect. Purchased, 1847. 
21975. Group of scales. 
41125. Small scale, inner aspect. 
15533. Small scale, inner aspect; Burdiehouse. 
21223 a. Group of scales; Burdiehouse. 
Purchased , 1848. 
Bryson Coll. 
Purchased. 
Purchased, 1847. 
