xX OSTRACODERMI—HETEROSTRACI 5 
No 
5 
from the Ludlow and Downtonian Beds of Lanarkshire.  De- 
tached scales are also known in the Upper Silurian of England. 
One species (7. page) occurs in the Lower Old Red Sandstone 
of Forfarshire, and another (7h. tulensis) in the Upper Devonian 
of Russia. Lanarkia has only been found in the Downtonian 
Beds. None of the Coelo- 
lepidae exceed fourteen to 
fifteen inches in length. 
Fam. 2. Drepanaspidae. 
—This family ' affords an in- 
teresting transition to the 
more highly specialised and 
carapaced Pteraspidae. The 
head and anterior part of the 
trunk now form a broad ob- 
long shield, rounded in front 
and abruptly marked off from 
the tail by conspicuous rounded 
angles. The exoskeleton is no 
longer uniform. In the caudal 
region the scattered spines or 
shagreen tubercles of the 
Coelolepids have become trans- 
formed into tuberculated quad- 
rangular scales, which are 
further differentiated along 
the dorsal and ventral margins 
into ridge scales or fulera; 
and from a similar source by a 
process of basal fusion a series 
of larger or smaller dermal 
plates are formed as com- 
ponents of large dorsal or 
ventral shields. The dorsal 
Fic. 314.—Restored outline of the dorsal sur- 
face of Drepanaspis gemiindenensis. The 
tail appears in profile. m.d, Median dorsal 
plate ; p./, postero-lateral plate ; 7, rostral 
plates. (From Traquair.) 
shield (Fig. 314) is formed by a large central plate; the 
postero-lateral portions by two narrow falciform plates; and 
the anterior margin by a 
series of smaller rostral plates. 
Between the larger plates the shield is completed by numerous 
1 Id. Trans. Roy. Soc. Edinb. xxxix. 1899, p. 844; Geol. Mag. vii. 1900, p. 153 ; 
ix. 1902, p. 289; Trans. Roy. Soc. Edinb. xl. Pt. iv. 1903, p. 723. 
