ESPECIALLY MYCTOPHOIDS 63 
Vertebral column. The vertebral column is shown in the reconstruction, Text- 
figure 28. It consists of approximately 60 vertebrae, of which 30 appear to be 
caudal. The first 18 precaudal vertebrae are of uniform size, as long as deep. 
Between the 18th and the 22nd a slight increase in vertebral length occurs but after 
the 22nd the centra remain constant with a length slightly in excess of their depth. 
The length of each vertebra decreases in the region of the 20th caudal vertebra. 
Each centrum is mesially constricted and on the longer centra the constriction 
is most noticeable. The characteristic feature of the precaudal region is the 
presence on each centrum of two pairs of prominent transverse processes. The 
processes are directed ventro-laterally and occur at either end of the centrum. The 
anterior transverse process is larger than the posterior. The processes remain 
relatively constant in size on the first 15 precaudal vertebrae, but posterior to this 
they begin to elongate and reach their greatest length at about the 22nd precaudal 
vertebra, 1.e. below the origin of the dorsal fin. Posterior to the 22nd vertebra the 
transverse processes gradually decrease in length and incline more ventrally. In the 
caudal region the anterior pair of transverse processes fuses ventrally to produce the 
haemal arches whilst the posterior pair appears to become zygapophyses. Ribs if 
present are very feeble and short, one or two centra do appear to have small fine ribs 
articulating with the underside of the larger, anterior, transverse processes. Long 
and low neural arches are present along the entire length of the column. Each 
neural arch occupies the whole dorsal extent of the corresponding centrum and gives 
rise to a feeble, posteriorly directed neural spine. These spines arise from the 
posterior region of each neural arch, and a prominent prezygapophysis is visible on 
the anterior region. The entire length of the body seems to have been provided 
with intermuscular bones, both epineurals and epipleurals, and possibly a certain 
number of epicentrals. Along a considerable part of the precaudal region in the 
mid-dorsal line there are several ossifications which are more substantial than the 
intermuscular bones. These may represent several median intermusculars com- 
pounded together, or, more probably, an ossified dorsal ligament. Just behind the 
occipital region of the head the anteriormost ossification appears to expand ventrally 
and connects with the neural spine of the first vertebra. 
Scales. The body is devoid of scales except for a single row on each flank, marking 
the course of the lateral line. All of the scales are based on a triradiate plan with a 
long forwardly projecting arm and two shorter divergent backwardly projecting 
arms. The interspaces between the smaller arms and the larger arm are variously 
filled with bone to give a more rounded outline which becomes more noticeable 
caudally. At the point of junction of the three arms a small backwardly projecting 
spine occurs: this is present on all the scales but is more pronounced and uncinate 
in the caudal region. 
RemMARKs. Arambourg’s (1954) description of the type species Rhynchodercetis 
yovanovitchi (Text-fig. 29) differs in a few details from the above description of 
Rhynchodercetis hakelensis. Arambourg’s supraorbital above the posterior end of 
the orbit does not appear to be a separate bone but merely the lateral extension of 
the frontal above the orbit. Here, as in specimens of other genera examined 
