ESPECIALLY MYCTOPHOIDS 93 
be branched. The number of rays contained in the fin is approximately 10. The 
position of the pelvic fins is abdominal, below the origin of the dorsal fin. 
Vertebral column. The vertebral column is shown in the restoration in Text-figure 
41. It consists of 37 vertebrae, of which 24 are caudal. The centra are slightly 
constricted mesially and are just longer than deep. The lateral face of each centrum 
bears a pronounced longitudinal ridge above and below which are prominent 
depressions. The neural arches occupy the entire length of the dorsal region of each 
centrum, and the neural spines emerge from the mid-dorsal region of each arch. 
The suture between the neural arches and the centra is always clearly visible. 
Anteriorly the neural arches have invariably become separated from the correspond- 
ing centra during fossilization indicating the looseness of this connection. More 
posteriorly the neural arches tend to be more closely attached to the centra. The 
precaudal vertebrae bear paired ventro-lateral transverse processes near the anterior 
end of each centrum. Pleural ribs articulate with these processes, the ribs them- 
selves being long and flattened, and tapering to a point. The first two or three 
caudal vertebrae have a haemal arch with a gradually lengthening haemal spine, but 
also bear articulated pleural ribs of reduced dimensions. The subsequent haemal 
arches bear longer backwardly directed haemal spines. 
Zygapophyses are present both above and below the column. The postzyga- 
pophyses are the more prominent dorsally, and the anterior zygapophyses are more 
prominent ventrally. 
Epineurals and epipleurals are associated with the first 20 vertebrae. 
Median fins and tail. The dorsal fin is positioned midway along the back and is 
composed of 16 rays, all segmented and all but the first branched. The first ray is 
shorter and stouter than the subsequent rays, the second is the longest. The 
rays decrease in size posteriorly. Each fin ray is supported by a pterygiophore, 
comprising an elongated proximal radial and a medial radial, the latter extending at 
a slightly oblique angle between the bases of adjacent fin rays. The distal radials 
are not distinguishable as separate elements, they are presumably incorporated 
into the fin ray bases. The more anterior proximal radials are expanded, especially 
the first which bears a large median keel projecting anteriorly. 
The anal fin is composed of 20 rays and is confined to the more posterior part of 
the body. As in the dorsal fin the first ray is short and unbranched, as opposed to 
the longer, branched and segmented, subsequent rays. The radial composition is 
like that of the dorsal fin except that the most anterior proximal radial is unexpanded 
and the medial radials are less pronounced. 
The caudal skeleton (Text-fig. 42) is composed of 6 vertebrae : three separate 
preural vertebrae (numbers 2, 3 and 4) ; a compound vertebra formed from the 
combination of preural vertebra I with ural vertebra r ; anda terminal half-centrum, 
the remains of ural vertebra 2. Preural vertebrae 3 and 4 bear slightly expanded, 
backwardly projecting neural and haemal spines which aid in the support of the 
accessory fin rays. The second preural vertebra (the first free preural vertebra) 
does not possess a neural spine, simply an expanded neural arch dorsally, and a 
markedly more expanded haemal spine ventrally. Preural vertebra 1 and ural 
