COCCOSTEID.E. 
281 
The course of the sensory canuls 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 ahetero- 
cercal manner. The neural and hasmal arches are short, robust, 
Outline of ventral armour of Coccosteus decipiens, Ag., restored by E. H. 
Traquair.— a.m.v., anterior median ventral; a.v.l., anterior ventro-lateral; 
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 hasmal 
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. 
