44 
CHIAIJEROIDEI. 
Rostral cartilage somewhat produced, bearing a terminal cutaneous 
flap. Mandibular tooth more or less massive in external appearance, 
though really a thin plate; symphysial surface narrow; oral surface 
undulating and covered by an extended, punctate, tritoral area, 
almost or quite continuous. Presymphysial tooth vertically elon¬ 
gated, bilaterally symmetrical, compressed antero-posteriorly, the 
inner aspect being flat or concave, the outer aspect convex. Pala¬ 
tine tooth thin, plate-like, triangular or irregularly quadrate in 
form, the outer margin being nearly straight, sharply deflected and 
thickened, the inner and posterior margins tapering gradually to a 
thin edge; oral aspect with a continuous, punctate, tritoral area. 
Vomerine tooth smaller than the palatine, of triangular form, broad 
posteriorly, and provided either with a long anteriorly-directed 
process or with a distinct small tooth in front; punctate tritoral 
area subdivided into rounded patches. Dorsal fin-spine long and 
slender, somewhat laterally compressed, with a large internal cavity ; 
sides more or less ornamented with small tubercles ; a series of 
large, thorn-shaped, spinous tubercles arranged along each edge of 
the flattened posterior face, passing into a single median row dis- 
tally, and a single series of similar denticles occupying at least 
part of the anterior border. Rostral spine of male elongated and 
pointed, Avith expanded base. Dermal plates tuberculated. 
Myriacanthus paradoxus, Agassiz. 
[Plate II. figs. 1-3.] 
1822. “ External defensive organ,” II. T. De la Beche, Trans. Geol. Soc. 
[2] vol. i. p. 44, pi. v. figs. 1, 2. 
1837. Myriacanthus paradoxus, L. Agassiz, Poiss. Eoss. vol. iii. p. 38, 
pi. vi. 
1837. Myriacanthus retrorsus , L. Agassiz, ibid. p. 39, pi. viii a. figs. 14, 
15. [Base of spine ; Oxford Museum.] 
1843. Chimcera (Ischyodon) johnsonii, L. Agassiz, ibid. p. 344, pi. xl c. 
fig. 22. [Dentition ; British Museum.] 
1872. Proyncithodus yuentheri , SirP. Egerton, Quart. Journ. Geol. Soc. 
vol. xxA'iii. p. 233, pi. viii. [Dentition; British Museum.] 
1889. Myriacanthus paradoxus, A. S. Woodward, Ann. Mag. Nat. Hist. 
[6] vol. iv. p. 279. 
Type. Dorsal fin-spines; British Museum and Bristol Museum. 
The type species, of large size, the dorsal spine attaining a maxi¬ 
mum length of not less than 06. Dorsal spine oval in section, 
flattened posteriorly, and with a faint anterior longitudinal ridge : 
lateral tuberculations relatively large and sparse, arranged on a 
longitudinally striated surface : anterior and posterior denticles very 
