120 Ctenoid Acanthopteres. FISHES. Uranoscopians 
bone they form being merely the substance called 
“osteoid” by Kblliker. The dermal or exo-skeleton 
exists generally in form of ctenoid scales, though some 
Acanthopteres have cycloid scales, and some are desti- 
tute of scales. The ventrals are situated in the great 
majority of the order on the thorax, and have a spine 
in front. The first dorsal, or when that fin is solitary, 
its anterior rays and the front rays of the anal, are 
spinous. In many, spinous angles or processes are 
developed on the cranial or opercular bones, there being 
a considerable variety of defensive armour exhibited 
by different members of the order. Normally the 
number of branching or jointed rays in the ventrals are 
five, but there are many exceptions, and some families 
want ventrals. The swim-bladder when present is 
closed. All the fishes of this order have a single gill- 
opening on each side, generally four pairs of double- 
ranked gills with free tips, and but one pair of valves 
at the root of the arterial bulb, guarding the ventriculo- 
arterial orifice, and no spiral rows of valves in the inte- 
rior of the bulb. The maxillary bone lies behind the 
extremity of the premaxillary, and does not constitute 
any part of the upper border of the mouth. 
The first sub-order of Acanthopteres has most gene- 
rally ctenoid scales, there being only a few exceptions 
in which the scales are small, tender, and cycloid ; but 
the other parts of their structure agreeing closely with 
the ctenoid genera, it has not been thought expedient 
to separate them. On the limits of the sub-order, 
genera and species destitute of scales occur. 
Sub-order I.— CTENOID ACANTHOPTEEES. 
Family I.— PSEUDOCHROMIDS {Pseudo- 
cliromidcc). 
The members of this group are scaly Acanthopteres, 
with a long dorsal fin, preceded by a few spines either 
in a detached fin, or joined to the soft rays by mem- 
brane. Their lateral line is interrupted ; the cheek is 
not cuirassed by the second sub-orbitar, and there are 
no sharp serratures or spines on the opercular bones. 
Branchiostegals six. 
The family includes the following genera — Ciahlops ; Pseu- 
dochromis; Pseudoplesiops (Bleeker); (Richardson). 
Fig 30 
Leather-headed Notothen (Nototheuia coriiceps). 
Notothenia is a genus of the high southern latitudes, 
discovered on the antarctic voyage of Admiral Sir 
James Clark Ross. 
Family II.— URANOSCOPIANS, or SKY- 
GAZERS. — (Plate 7, fig. 35.) 
This family group, equivalent to the Trachinidai of 
Bonaparte, consists of fishes whose ventrals of one 
spine and five soft rays are situated before the pectorals, 
or close behind them, and which have either a naked 
skin, or scales of cycloid structure. The vent is gene- 
ralh’ before the middle of the fish, so that the tail 
exceeds the body in length. The caudal is distinct 
from the other vertical fins, and the spinous dorsal is 
usually abbreviated, and sometimes absent. A pro- 
jection of the mandible in some genera gives a vertical 
aspect to the orifice of the mouth, which is always 
terminal, and is bordered above its angles by the pre- 
maxillaries to the exclusion of the maxillaries. No 
sharp points or serratures exist on the sub-orbitar or 
preopercular pieces, but in some cases a strong spine 
issues from the surface of the operculum or from the 
shoulder-bone. The branchiostegals generally number 
six or seven ; more rarely five. Occasionally the 
cavity of the abdomen is prolonged past the vent into 
