536 



FISHES 



CHAP. 



B 



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. Gill-arches are not known. 

 A pair of plates (Fig. 324, A, j} 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 ranius. 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 * am. 1. UOCCOSteidae. 



ventral part of the trunk armour (B). a.d.l, CoMOStcUS OCClirS in the 



Anterior dor-so - lateral ; a. I, antero - lateral ; f TT A 



a.m.v, anterior median ventral ; a.v.l, anterior -Devonian. OI Europe and. 



ventro-lateral ; c, central; e.o, external occi- ]^"orth America and in- 



pital ; i.l, internal lateral ; j, jugal ; m, marginal ; 



m.d, median dorsal ; m.e, dermal mesethmoid ; eludes Species Ot relatively 



TO.O, median occipital ; m.v, median ventral ; mx, g^iaH size not exceedin " 



maxilla ; n, nasal aperture ; o, orbit ; p, pineal ' 



plate ; 2).d.l, posterior dorso-lateral ; p.mx, pre- halt a metre in length. C. 



maxilla; po, preorbital ; pt .0 post - orbital ; d ec i p i ens t he best known 



p.v.l, posterior ventro-lateral. (trom. Iraquair.) - 1 - ' 



species, is a characteristic 



fossil in the Old Eed Sandstone of Scotland. Plilyctaenaspis l 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 Eed Sandstone of the North of Scotland, 

 and in the Devonian of Germany and Eussia. 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. 3 



1 Traquair, Geol. Mag. (3), vii. 1890, p. 55 ; Proe. Roy. Phys. Soc. Edinb. x. 

 p. 227. 2 Id. Geol. Mag. (3), vi. 1889, p. 1. 



3 Newberry, The Palaeozoic Fishes of North America, Mon. U. S. Geol. Survey, 

 xvi. 1889 ; Bash ford Dean, Fishes, Living and Fossil, Xew York, 1895, p. 129 

 et seq. ; New York Acad. Sci. Mem. ii. 1901, p. 87 ; Eastman, Amer. Journ. Sci. 

 (4), ii. 1896, p. 46 ; Amer. Geol. xviii. 1896, p. 222 ; Bull. Mus. Comp. Zool. xxxi. 

 1897, p. 19. 



