BELONORHriTCHTDJE. 
15 
powerful; superficial ornament consisting of short rugae, the 
majority directed longitudinally. Operculum two-thirds as broad 
as deep. Scutes of dorsal and ventral series long, narrow, and 
slender, apparently smooth. 
Form. Sf Log. Upper Lias : Yorkshire. Lower Lias : Dorsetshire. 
Except the first, all the following specimens were obtained from 
Lower Lias of the neighbourhood of Lyme Regis. 
P. 4268. Type specimen, being the fragmentary cranium figured by 
Agassiz, loc. cit. fig. 4; Upper Lias, Whitby. 
Enniskillen Coll. 
P. 428. Crushed and somewhat fractured head, lateral aspect, 
measuring 0T45 in length, but wanting the extremity of 
the snout. The laniary teeth gradually become more and 
more robust backwards, and those of the two jaws alternate, 
fitting into broad notches; the clusters of minute inter¬ 
vening denticles are conspicuous. The imperfectly pre¬ 
served angular bone of the mandible is shown to be 
continuous with the articular element. Purchased , 1882. 
43054. Smaller head, 0*1 in length, the cranium much crushed but 
showing the extension of the roof-bones beyond the 
occiput posteriorly. The jaws are almost of equal length, 
the mandible being not more than 0*002 shorter than the 
upper jaw. The angular boDe displays its truncated but 
gently rounded postero-inferior border, and also exhibits 
the series of vertically-extended markings due to the per¬ 
forations of a sensory canal. Purchased , 1871. 
P. 3791. A fine example of the head, with left operculum and 
clavicle, shown of the natural size in PL II. fig. 1. Be¬ 
sides displaying the general proportions, this specimen 
also exhibits a few details, notably the post-occipital 
extension of the cranial roof (?-.), the presence of cheek- 
plates, the position of the narial opening (n.), and the 
form of the articulo-angular bone. The operculum (op.) is 
nearly one and a half times as deep as broad, tapering 
downwards, and evidently not succeeded either by a sub¬ 
operculum or branchiostegal rays. The clavicle (cl.) is 
deep, narrow and gently arched, with a relatively large 
but narrow triangular plate extending far backwards from 
the hinder border. Enniskillen Coll. 
P. 965. Somewhat smaller head, lateral aspect, with operculum and 
clavicle. Egerton Coll. 
