4 
(Fig. 4) are elongate-oval in shape, the pointed end being directed inwards, 
while the outer blunt end beais the usual “ button ” for articulation with the 
next outer tooth which it overlaps. The two principal cones of the dental 
crown (Figs. 3, 5) are round in section, gently incurved, and apparently 
smooth. They are hollow and easily broken, and fractured surfaces impart 
to some specimens the false appearance of vertical ribbing. Between the 
principal cusps there is a long and slender, straight denticle, which is also 
hollow and often broken. 
Branchial Arches . — As usual in Fleur acanthus, the branchial arches 
bear well-developed cartilaginous rays for the support of the gills. Some of 
these are well shown behind and below the mandible in PI. I, Fig. 2, 
where the smaller and more delicate rays (g. 1 ) probably belong to the 
ceratohyal, while a stouter scries (g. 2 ) must be referred to the first branchial 
arch. The middle members of the latter series are shown as branching, but 
it is uncertain whether this is not a false appearance due to displacements 
during fossilisation. 
Vertebral Axis . — The persistent character of the notochord is clearly 
indicated in the type specimen (PI. I, Fig. 1), in which the haemal arches are 
probably a little displaced downwards by crushing. The arches themselves 
are all well calcified in tesserae, though the small hollow frequently seen in 
the middle of both neural and haemal elements proves that this calcification 
did not penetrate quite to the centre of the cartilage. Seven comparatively 
stout and forwardly inclined neural arches are shown in advance of the 
remains of the pectoral girdle, while appearances in the hinder four of these 
arches suggest that the neural spine (s.) is a separate element and as long as 
the supporting pair of laminae. There cannot be more than one additional 
arch of this series covered by the upper end of the scapula, and then the 
normal series of backwardly-inclined, slender neural arches begins. These 
arches do not diminish in height until the caudal region is reached, and 
owing to their slenderness they are variously crushed and broken. In the 
abdominal region (PI. I, Fig. 6) the laminae of each arch (na.) are wide at 
the base, where those of successive segments are in close contact ; but they 
rapidly become slender in their upper half, where they may have been 
surmounted by a separate neural spine. The right and left laminae are often 
displaced, so that both are partly exposed in side-view ; and the numerous 
fractures and dislocations render it difficult to decide whether or not the 
upper part of the arch is really a distinct element. In the caudal region 
