ON SOME ARMOUKED FISHES. 
9 
near to Scaphaspis , its outline and profile* are more like those 
of Pteraspis. 
Pteraspis (Woodcut, Fig. 5), is the last and most highly 
developed of the Heterostracous fish-shields. 
The shield is much more pointed than the other forms, re- 
sembling a javelin-head in shape, and is divisible by sutures 
into seven parts. The dorsal spine is strongly developed, and 
the small marginal orbits (o, o,) are distinctly visible. The 
palm-like wrinklings upon the surface are not unfrequently 
beautifully preserved. 
Pteraspis has only three species, but they are found in 
Monmouthshire, in Shropshire, at Malvern, Worcestershire, in 
Herefordshire, and in Forfarshire, Scotland; all in the Lower 
Old Red Sandstone formation. 
Professor Schmidt, of St. Petersburg, has described another 
Russian form, under the name of the Tremataspis , but we have 
not yet seen its figure or description. 
Of the Osteostracous forms of head-shields that best known 
to palaeontologists is the genus Cephalaspis (PI. I., Fig. 4), 
established by Agassiz in his great work in 1835.f In this 
genus the posterior angles of the shield-shaped helmet are pro- 
duced backwards in a pointed form, giving to the head the out- 
line of a “ saddler’s knife ” — u a too] with a crescent-shaped 
blade, and the handle fixed tranversely in its concave side. In 
general outline the Cephalaspis resembled this tool, the cres- 
cent-shaped blade representing the head, the transverse handle, 
the body. The head compared with the body was of great size, 
comprising nearly one-third of the creature’s entire length. In 
the centre, and placed closely together, as in many of the flat 
fishes, were the eyes.”J The fins consisted of two pectoral fins 
of very peculiar form and character (PI. I., Fig. 4, y>), a 
dorsal fin ( d ), placed very far back on the body, and a caudal 
fin, the rays of which are all placed inferiorly to the extremity 
of the body (c). 
The pectoral fins have no trace of fin-rays or scales : they are 
simply ellipsoidal expanses, with some calcareous matter in their 
structure which has caused their preservation. 
The body, which was triangular in form, was protected by four 
principal rows of imbricated rhomboidal scales, with a lower 
marginal row and probably eight rows of small ventral scales ; 
the bony structure of these scales accords with tha t of the head- 
shield. The scales break up, and become smaller and much 
* “ Geol. Mag.” 1873, Vol. x. p. 331 (woodcut). 
t 11 Poissons Fossiles du Vieux Gres Rouge, ou System e Devonien: Xeuf- 
chatel.” Folio plates, 4to. text ; Yol. ii. 1835, p. 149. 
X Hugh Miller, “The Old Red Sandstone,” 1847, p. 172. 
