No.1; MORPHOLOGY OF CLADOSELACHE. 89 
In the arrangement of his paper, the writer has for con- 
venience, considered questions of relationship under structural 
headings. 
THE AXIAL SKELETON. 
The notochord was probably persistent and its surrounding 
tissue but little calcified. In the trunk no traces of its 
structures have been found. Its caudal termination is, 
however, well shown; in this region its substance is compact, 
finely granular (Fig. 3), lacking the sheath constrictions of 
Pleuracanthus and Chondrenchelys.2. In the upper lobe of 
the tail the chorda narrowly tapers, and extends to the 
extreme tip. As will be later noted, the hypural rod-like 
supports are here lacking, replaced by an unjointed sub- 
notochordal rod of semi-calcified cartilage. Of the neural 
canal in this region little can be learned; its size must 
have been exceedingly minute, judging from the close origin 
of the epural supports to the notochord. From the type of 
chord thus suggested it is not unreasonable to infer that 
the vertebral arches, of which no traces have been found, 
must have been of the simplest type, certainly as primitive as 
those known to occur in //ybodus. In no part of the axial 
skeleton has the writer found the coarse beaded calcifications 
typical of the ‘Ichthyotomi.’ In general calcification appears 
centripetal, is marked in basal fin rays, jaws, skull and shoulder 
girdle. The head parts appear generally similar in character to 
those of Chlamydoselache. There is no evidence of what were 
described by Cope as cranial elements in the Permian Dzdy- 
modus,'5 nor of the “parasphenoid”’ of Chondrenchelys. The 
mouth was terminal, not as large proportionally as that of 
Chlamydoselache. The shape and disposition of the man- 
dibular rami indicate a narrow and pointed snout; at the 
symphysis, however, their proportions appear to have been 
heavier than of Chlamydoselache. Relatively the nares and 
eye capsules were slightly further forward. The orbit could 
have been little anterior to mandibular articulation — and 
suggests, therefore, a short down-turned suspensorium, From 
present material there is no evidence of a post-orbital facet for 
