1078 
S C AND I N A V I A N FIS II ES . 
EL ASMOBRAN CHII HOLOCEPHALI. 
Elasmobranchs with one gill-opening' common to all the gill-slits on each side of the body. No spiracles. Skin 
smooth, without placoid scales (spines''). Notochord unaltered, not constricted by the formation of vertebrae, 
only with superficial rings of cartilage, considerably exceeding in number the vertebral spaces (polyspondyli). 
Palatoquadrate part not divided from the skull, but furnished like the lower jaw with dental disks. 
That course of development from the primordial 
fishes' which is represented in the present age by the 
Holocephali , the suborder of the Chiimeras, has been 
arrested as regards the structure of the spinal column 
at a lower stage than the Plagiostoms. It is probable 
too that the structure of the palate in the Holocephali 
is a relic of the said ancestral types; but only the 
history of evolution can decide whether the union be- 
tween the palatoquadrate parts and the skull, a pecu- 
liarity which we shall again meet with in the still 
more primitive Marsipobranchs, is here of a primary 
or a secondary nature. Equally indispensable is the aid 
of the history of evolution to a determination whether 
the absence of spiracles is original or rather the con- 
sequence of reduction. Solgek has described in Chi- 
mcera monstrosa small cartilages (tig. 294, s) which 
occupy in relation to the lower jaw the same position 
as that assumed in relation to the palatoquadrate car- 
tilage by the spiracular cartilages (supports of the spi- 
racular gills) common in the Plagiostoms. It may 
reasonably be assumed that these so-called Solgerian 
cartilages admit of interpretation as vestiges of aborted 
spiracular gills. On the other hand, the structure of 
the branchial cavity in the Holocephali more clearly 
indicates a higher degree of differentiation, a step in 
the direction of the Chondrosteans and Teleosts. 
The Holocephali are marine and deep-sea fishes 
with a wide geographical range. How great is their 
geological age, can hardly be stated at present with 
certainty, for ichthyologists have supposed** that remains 
of these fishes have been discovered even in Devonian 
deposits. It is certain, however, that they lived in the 
Jurassic period, when its very earliest stratum (the 
Lias) was formed; and during the latter part of this 
period they attained a size far surpassing that of mo- 
dern Holocephali. Townsend, for instance, found in 
the Portland chalk at Great Milton (near Oxford) an 
under tooth of Chimcera ( Ischyodon ) Townsendii e that 
measured 1 1 cm. at the symphyseal margin, a dimen- 
sion which in a Chimcera monstrosa 75 cm. long is 
represented by 14 mm. 
The suborder contains only one family. 
Fa m. CHIMiERXDiE. 
Body of a compressed clavate form , most nearly resembling that of the Macruroids. Dentition of the mouth made 
up of two upper pairs and one under pair of dental plates , most similar to those of the Lung-fishes {Dipnoi). 
Two f dorsal fins , the anterior , above the pectoral fins , triangular and armed with spines , the posterior low and 
long; a small , sometimes scarcely distinguishable anal fin, situated far back; caudal fin diphy cereal or heterocefical . 
Of this family only four* * 7 species survive at the pre- which, the Antarctic Callorhynchus, contains a solitary 
sent time. These have been ranged in two genera, one of species and is characterised by the more obliquely for- 
0 blog, tvhole, and VM'fiaifi, head. 
b In the young of Callorhynchus (a genus from the Pacific Ocean and the Antarctic regions) spines have been found in two longitu- 
dinal rows, partly on the forehead, partly on the back, between the first and second dorsal fins (see Dum., Hist. Nat. Poiss., Suites a Buffon, 
tome I, p. G94, pi. 14, fig. 4), an indication that the skin of the primitive forms was clothed with spines. 
c Pisces aspondyli, PIasse, Nattirl. Hyst. Elasmobr., Allgem. Tbeil, p. 31. 
d Of. Gunther, Introd. Study Fish., p. 349. 
e Agassiz, Rech. Poiss. Foss., tome III, p. 343, tab. 40, fig. 20. 
• f Sometimes the posterior dorsal fin is so deeply sinuous that three dorsal fins have been counted. 
9 Gill has besides described a Chimcera phnnbea from the Atlantic coast of North America; but there would hardly seem to be any 
specific distinction between this form and our Chiinsera. 
