﻿DIPLACANTHID^. 



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, fy 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). 



d2 



