DIPLACANTHIDiE. 
35 
A species of larger size than P. incurvus ; head very large, occu¬ 
pying one third of the total length. Pectoral fin-spines short, stout, 
and curved ; four pairs of short and broad, small, intermediate 
ventral spines; pelvic fin-spines about two thirds as long as the 
pectorals, much less robust. First dorsal spine very stout and much 
curved, with few, widely spaced, posterior denticles, about one third 
as long as the complete fish and situated immediately above the 
pectoral arch; second dorsal spine about one half as long as the 
first, placed immediately in advance of the anal, which it somewhat 
exceeds in size. Scales externally tuberculated. 
Form, Log. Lower Old Red Sandstone : Forfarshire. 
P. 130. Imperfect fish, wanting the head, the extremity of the tail, 
and the first dorsal fin-spine ; Turin Hill, near Forfar. 
The abdominal region is shown from the ventral, and the 
caudal region from the lateral aspect. The pectoral arch 
Fig. 4. 
Pectoral fin and half of pectoral arch of Parexus falcatus, Powrie. — b, basal 
cartilage; cl, clavicle ; s, spine. 
and spines are shown from beneath, and the elements of 
the left side are represented in a somewhat diagrammatic 
manner in the accompanying woodcut. The pectoral arch 
consists of a pair of thin, triangular or sickle-shaped 
elements (fig. 4, cZ), meeting in the middle line, and the 
inferior limb apparently as large as the ascending limb; 
as shown in the figure, the latter is crushed so as to be 
directed backwards. The squamation on the ventral aspect 
between the pectoral fins is much enlarged and covers an 
anteriorly narrowing triangular area to the point of 
meeting of the two halves of the pectoral arch in the 
median line ; and this arrangement of the scales in direct 
relation to the latter suggests that the elements preserved 
fall within the category of membrane-bones (clavicles). 
n 2 
