﻿COCCOSTEID -35. 28 1 



The course of the sensory canals is well marked upon the plates 

 both of the head and trunk by deep grooves, which have often been 

 mistaken for sutures. They were first clearly mapped by Traquair 

 as dotted lines on the accompanying figures. 



The hinder abdominal and caudal regions are destitute of armour 

 (fig. 44), the only dermal calcification occurring in a narrow band 

 along the lateral line (see p. 289). 



A narrow vacant space in the position of the notochord bears 

 witness to its persistence, and the tail tapers apparently in a hetero- 

 cercal manner. The neural and haemal arches are short, robust, 



Fig. 43. 



Outline of ventral armour of Coccosteus decipiens, Ag., restored by E. H, 

 Traquair. — a.m.v., anterior median ventral ; a.v.l., anterior ventrolateral ; 

 i.L, inter-lateral (? clavicle); m.v., median ventral ; p. v.L, posterior ventro- 

 lateral. 



and closely arranged, fused with their respective spines, and all 

 superficially calcified. There are no ribs ; but immediately behind 

 the termination of the abdominal region the neural and haemal 

 arches gradually become elongated for some distance, and to the 

 ends of the long neurals in this part of the axis are apposed, in 

 equal number, the basal cartilages of a short dorsal fin. The latter 

 cartilages occur in two rows, a proximal and a distal, the elements 

 all being superficially calcified and as robust as the neural spines. 

 The fin itself was membranous, and is partly shown by an Orkney 

 fossil (No. P. 180) mentioned below (p. 285), but still more satis- 

 factorily in a single specimen in the University of Glasgow. There 

 is no anal fin, and a caudal has not yet been recognized. 



