ESPECIALLY MYCTOPHOIDS 187 
backwardly projecting haemal spine. Intermuscular bones, both epineurals and 
epipleurals, are present on the first 26 vertebrae. 
Median fins and tail. The median fins are shown in the restoration, Text-figure 85. 
The dorsal fin consists of approximately 18 rays and occurs about mid-way along the 
length of the body. The first ray is unbranched and shorter than the subsequent 
rays which are all branched and segmented. The proximal radials are elongate 
and the anteriormost are expanded, especially the first which bears a large forwardly 
directed keel-like expansion. The heads of all the proximal radials are expanded. 
Certain of the narrow medial radials are visible extending horizontally between 
the bases of adjacent fin rays. 
The anal fin is made up of 14 rays and positioned at the extreme posterior end of 
the body close to the caudal fin. As in the dorsal fin the first ray is unbranched. 
The proximal radials are prominent and elongate but not expanded. Medial radials 
occur between the bases of adjacent fin rays. 
The caudal skeleton is composed of 6 vertebrae. There are three free preural 
vertebrae (preurals 2, 3 and 4) ; one fused preural and ural vertebra (preural 1 and 
ural 1) ; and one free ural vertebra (ural 2) which is represented by a terminal half- 
centrum. Preurals 3 and 4 bear normal neural and haemal spines, whereas preural 
2 bears an expanded haemal spine and only a neural arch, the neural spine having 
been lost. The compound vertebra (preural I + ural I) bears the parhypural 
(haemal spine of preural 1) and two hypurals, the first of which is the larger. Ural 
vertebra 2 has approximately three hypurals associated with it making at least five 
hypurals in all. Associated with the dorsal regions of the ural vertebrae are two 
uroneural elements, which are elongated in a postero-dorsal direction. At least two 
epural elements are present, one of which is expanded. 
Nineteen principal fin rays are present of which 17 are branched. Accessory fin 
rays are present above and below the fin and number at least 20. 
Scales. Several of the scales are shown in the inset to Text-figure 85. They are 
present as a single continuous row along the lateral region of the body, and represent 
much enlarged lateral line scutes. The scales begin immediately behind the supra- 
cleithrum and terminate on the caudal peduncle. The row consists of 45 scutes, the 
most anterior and posterior ones being the smallest. Most of the scutes are about 
three times as deep as they are broad and the lateral line canal ran within their 
centres. The scales overlap and posteriorly are irregularly serrated. In the region 
of the lateral line there is a somewhat deeper indentation of the rear margin which is 
overhung by a backwardly projecting spine. The anterior edge of each scale is 
thickened and dorsally and ventrally the edges are rounded. The scales are 
obliquely inclined and ornamented with ridges on their exposed portions. The 
posterior part of the lateral face bears horizontally arranged ridges, whilst the 
anterior regions have vertically arranged ridges. Towards the caudal peduncle the 
scales become reduced in depth but the backwardly projecting spines become more 
prominent so that pronounced lateral flanges are produced on either side of the tail. 
From the above description it can be seen that Prionolepis does share certain 
common characteristics with the Cimolichthyoidei. The skull roof is similar, with 
