214 
ANTI ARC HA, 
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.d.) 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 
(g.d.l.); and the usual constriction near the hinder 
extremity of the posterior ventro-laterals (p.v.l.) 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 Enniskillen Colls. 
28858. Portions of head and trunk, with pectoral appendages. 
Purchased , 1854. 
P. 659. Tail, labelled P. latus by Agassiz, showing dorsal fin 
accidentally divided and appearing as if a pelvic pair; 
noticed by It. 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 , 1863, 
