﻿214 AXTIARCHA. 



extra-laterals (e.l.) are also shown, almost in their natural 

 position. As far as the hinder margin of the anterior 

 median dorsal plate, the roof of the carapace is preserved, 

 but more posteriorly the posterior ventro-laterals are 

 exposed from the visceral aspect, and the posterior median 

 dorsal plate is seen only in impression in the counterpart. 

 The anterior median dorsal (a.m.cl.) is slightly narrower 

 in front than behind, and its longitudinal keel rises to a 

 prominent apex in the centre. The anterior dorso-lateral 

 plates (a.d.l.) distinctly overlap the posterior dorso-laterals 

 (p.d.l.); and the usual constriction near the hinder 

 extremity of the posterior ventro-laterals (p. v. I.) is well 

 seen. The cycloidal scales of the tail exhibit no features 

 worthy of special note ; and the large fulcral scale at the 

 anterior margin of the dorsal fin {d.), though preserved, 

 is apparently much broken. Purchased, 1879. 



50110. Individual with incomplete head, preserved in counterpart, 

 and shown of the natural size in PI. V, fig. 4. Many of 

 the plates are distinctly exhibited, notably the right 

 posterior ventro- lateral ; and the form and proportions of 

 the pectoral appendages are indicated. Towards the 

 extremity of the tail occur traces of the dorsal fulcral 

 scales (/.) ; and a ferruginous stain may indicate the 

 original presence of a terminal fin, or may be merely an 

 aggregation of mineral matter round the point. 



Purchased, 1879. 



P. 6262. Portions of the head and pectoral appendages, and the 

 ventral plates seen from the visceral aspect. 



P. 658, P. 3204. Two examples of the imperfect trunk, in counter- 

 part, ventral aspect. Egerton 6f EnnisTcillen Colls. 



28858. Portions of head and trunk, with pectoral appendages. 



Purchased, 1854. 



P. 659. Tail, labelled P. latus by Agassis, showing dorsal fin 

 accidentally divided and appearing as if a pelvic pair ; 

 noticed by R. H. Traquair, Geol. Mag. [3] vol. v. p. 509. 



Egerton Coll. 



(iii.) Tynet Burn (typical P. latus). 

 37985. Imperfect head and trunk, displaying several plates. 



Purchased, 1S63. 



