40 WOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 
behind, distantly articulated nearly to the base and most shown to 
be divided distally ; its anterior border is fringed with minute fulcra. 
The pelvic fin on the left side {ph.) is similar but smaller, with only 
about sixteen rays. The series of scales seem to correspond with the 
myocommata of the trunk, but they are modified between the bases 
of the fins ; whereas the angle the series make in the median line 
points backwards as a rule, the direction suddenly changes between 
the pectoral fins. Moreover, the short basal lobe of the pectoral fin 
is shown to be invested on its inner face with comparatively small 
scales {b.) ; while bordering this lobe within is a longitudinal series of 
slightly enlarged scales {x.), all apparently about as broad as long. 
Between the pelvic fins there are also at least two enlarged scales 
ip.x.), but they are somewhat fractured and their outline is not 
quite clear. 
Another fragment (Brit. Mus., No. 35580) exhibits the dorsal fin 
consisting of more than twenty stout rays, some of the basal joints 
with traces of an ornament of longitudinal ridges. 
The specific characters of the Whitby Ptycholeins may thus be 
enumerated as follows : — 
The type species, attaining a length of about 0*35 m. Length of 
head with opercular apparatus equalling the maximum depth of the 
trunk and nearly one-quarter of the total length of the fish. The 
ridged ornament of the head coarse, very rarely mingled with few 
tubercles, and covering all the external bones except the gular plate 
and branchiostegal rays, which are nearly smooth ; the supraclavicle 
also ornamented with finer transverse ridges. Most of the ridges on 
the cranium, cheeks, and opercular bones longitudinal ; the ridges 
on the upper portion of the dentary and hinder half of maxilla 
oblique. The stouter fin-rays ornamented with few fine longitudinal 
ridges of ganoine ; pelvic fins arising midway between the pectorals 
and the caudal ; dorsal fin with slightly more than twenty rays, 
arising well in advance of the pelvic pair. Scales marked with from 
one to four or five delicate, irregular, longitudinal furrows, sometimes 
discontinuous, sometimes branching, rarely reaching the hinder 
border except on the middle of the abdominal flank, and producing 
an ornament of large, incomplete, rounded ridges ; the hinder border 
deeply and coarsely denticulated. 
