130 ARTHRODIRAN LUNG-FISHES 
doselachian sharks. As recently as 1887 its members were 
associated by Traquair with Pterichthys, but the discovery 
of jaws, specialized dentition, fin spines, and highly evolved 
pelvic fins at once separate this group from the lowly 
Ostracoderms. | 
American Arthrodirans, described mainly by Newberry 
and by Claypole, have proven of especial interest. They 
occur from the Silurian to the Coal Measures. The giant 
predatory member of this group, Dinichthys (Frontispiece, 
and Figs. 133-137), attained a length of ten feet. TZ7Ztan- 
ichthys, less formidable in armour and dentition, may well 
have been twenty-five feet in length. These forms occur 
almost exclusively in the Waverly of Ohio. Their discovery 
has here been due to the efforts of Dr. William Clark 
of Berea, Rev. William Kepler of New London, and Mr. 
Jay Terrell of Linton; and most of the type specimens 
have been preserved in the museum of Columbia College, 
New York. 
The European member of this group is a small, fresh- 
water (?) form, Coccosteus, especially abundant in the Old 
Red Sandstone of Scotland. It has thus far yielded the 
most complete material for study, and its structural char- 
acters might accordingly be described, since they are 
probably common to all members of the group. 
The lateral view of Coccosteus is shown in Fig. 130, the 
dorsal aspect of the anterior region in Fig. 131, and the 
ventral view of the visceral region in Fig. 132. It will 
accordingly be seen that the general shape of the body 
of this Arthrodiran was somewhat depressed; that the © 
head, shoulder, and stomach regions were protected by 
bony plates; and that the trunk region was lacking in 
armouring, and short in relative length. In well-preserved 
fossils the space occupied by the notochord, J, is seen to 
