FISHES CHAP. 
536 
that there are well-developed and partially calcified neural and 
haemal arches associated with a persistent notochord. It is 
possible that the skull is autostylic. Gifl-arches are not known. 
A pair of plates (Fig. 324, A, 7) at the postero-lateral angles of 
the cephalic shield may perhaps be opercula. The teeth are 
conical. Those in the upper jaw are supported by two pairs 
of plates, probably vomers 
and palatines. In the 
lower jaw there are two 
series of teeth, one in front 
near the symphysis, and 
the other behind, sup- 
ported by a single bone in 
each ramus. There is a 
well-developed lateral line 
system, indicated by sur- 
face markings on the head 
and trunk shields, 
Fig. 324.—Dorsal view of the cephalic and trunk 
shields of Coccosteus (A); and a view of the 
ventral part of the trunk armour (B). a.d.J, 
Anterior dorso- lateral ; a@./, antero - lateral ; 
a.m.v, anterior median ventral; a.v./, anterior 
ventro-lateral ; c, central; e.0, external occi- 
pital ; 7.2, internal lateral ; 7, jugal ; m, marginal ; 
m.d, median dorsal ; m.e, dermal mesethmoid ; 
m.o, median occipital ; m.v, median ventral ; mz, 
maxilla ; 7, nasal aperture ; 0, orbit ; », pineal 
plate ; p.d./, posterior dorso-lateral ; p.mx, pre- 
Fam. 1. Coccosteidae. 
—Coccosteus occurs in the 
Devonian of Europe and 
North America, and in- 
cludes species of relatively 
small size, not exceeding 
half a metre in length. C. 
maxilla; p.o, preorbital ; pt.o, post-orbital ; 
p.v.l, posterior ventro-lateral. (From Traquair.) deciprens, the best known 
species, is a characteristic 
fossil in the Old Red Sandstone of Scotland. Phlyctaenaspis* is 
found in the Lower Devonian of Canada, England, and Poland. A 
larger Arthrodiran, with slender toothless jaws, Homosteus,’ is met 
with in the Lower Old Red Sandstone of the North of Scotland, 
and in the Devonian of Germany and Russia. The Old World 
Arthrodira must yield, however, to those of the New World for 
variety in size and shape, and in the character of their dentition.° 
1 Traquair, Geol. Mag. (3), vii. 1890, p. 55; Proc. Roy. Phys. Soc. Edinb. x. 
1h 2 2 Id. Geol. Mag. (3), vi. 1889, p. 1. 
3 Newberry, The Palaeozoic Fishes of North America, Mon. U.S. Geol. Survey, 
xvi. 1889; Bashford Dean, Fishes, Living and Fossil, New York, 1895, p. 129 
et seq.; New York Acad, Sci. Mem. ii. 1901, p. 87 ; Eastman, Amer. Jowrn. Sei. 
(4), il, 1896, p. 46; Amer. Geol. xvili. 1896, p. 222; Bull. Mus. Comp. Zool. xxxi. 
ULV G joy, ile 
