36 
CHOOSKOIDEI. 
The basal cartilage (5) of the fin is evidently almost as 
long as the upper part of the supposed clavicle, with a very 
broad, triangular, distal extremity, meeting the obliquely 
truncated, attached end of the pectoral spine (s), and ter¬ 
minating in a very slender, rounded, proximal half. The 
fin-membranes are shown both in connection with this 
and all the other fin-spines; and there are four pairs of 
broad, intermediate ventral spines, increasing in size 
posteriorly. Purchased , 1880. 
Subclass II. HOLOCEPHAL1. 
Skeleton cartilaginous, membrane-bones absent. Mandibular sus- 
pensorium and upper jaw fused with the cranium. Exoskeleton, 
when present, structurally identical with the teeth. In the living 
forms—optic nerves not decussating, bulbus arteriosus of the heart 
with three series of valves, intestine with a spiral valve, and ovaries 
with few large ova. **<*•&, ,<f2 f 
2s . /rt( /'l r. X 5 C 4^. 
Order CHIM.EROLL)EI. 
Notochord persistent or partially constricted, the calcifications in 
the sheath, when present, consisting of slender rings more numerous 
than the neural and haemal arches. Pectoral fins shortened, without 
segmented axis ; pelvic fins produced into a pair of claspers in the 
male. In the living forms—a fold of skin covering the gill-clefts, 
and leaving a single external opening to the gill-cavity. 
In all the known families of Chimaeroids, the dentition consists 
of few large plates of vascular dentine, of which certain areas 
(“ tritors ”) are specially hardened by the deposition of calcareous 
salts within and around groups of medullary canals, which rise at 
right angles to the functional surface. In most cases there is a 
single pair of such plates in the lower jaw, meeting at the sym¬ 
physis, while two pairs are arranged to oppose these above. As a 
whole, the dentition thus closely resembles that of the typical 
Dipnoi (as has often been pointed out) ; and the upper teeth may 
be provisionally named palatine and vomerine until further dis¬ 
coveries shall have revealed their precise homologies. The struc¬ 
tures are sometimes described as “jaws,” and regarded as dentaries, 
maxillfe, and premaxilke, but the presence of a permanent pulp 
