196 PALEOZOIC FISHES OF NORTH AMERICA. 
Another, and in some respects very different, kind of Elasmobranch 
spine, represented by several species, has been described by Mr. Orestes 
St. John under the name of Physonemus.' These are relatively broad and 
strong spines, sometimes ten or twelve inches long, the broadly conical 
summit alone being solid, the middle and lower portions of the convex bor- 
der being opened by a deep furrow, on either side of which the margins 
thin to feather-edges; the sides and concave border are comparatively 
smooth and without ornamentation of any kind. About one-third of the 
length from the basal extremity the concave margin is raised and expanded 
to form a marked, sometimes swollen and overhanging shoulder, which in 
greater or less development is a conspicuous character in all the species. 
In the numerous and carefully drawn figures* the aspect and structure of 
this singular group of spines are well represented. It will be seen by refer- 
ence to these figures and the accompanying descriptions that the exterior 
surface is represented as plain, and it is supposed by Mr. St. John that it 
was once covered with enameled tubercles, which have all been removed. 
I have recently had an opportunity of examining about fifty spines col- 
lected by Dr. W. Clark from the Berea grit, the central member of the 
Waverly group (Lower Carboniferous), at Berea, Ohio, which throw new 
light upon the structure and position of this group of defenses. These spines 
apparently all belong to one species, which closely resembles Physonemus 
Altonensis,® St. J. & W., attaining about the same size, viz, from six to ten 
inches in length; the only marked difference between the spines obtained 
from Berea and those from Alton being that in the most complete Berea 
specimens the shoulder on the concave margin is much thicker and broader 
and is somewhat bilobed. All these specimens possess, however, some feat- 
ures which either are not present in those from the Carboniferous limestone 
of Illinois or have been overlooked by Mr. St. John, viz: (1) they are all un- 
symmetrical, the deep sulcus of the convex side is not central, one of its 
walls being thicker and broader than the other; (2) they are rights and lefts; 
in a large number it is easy to see that they may be somewhat equally 
divided into pairs. This means that they did not belong to the dorsal but 
to the paired fins, the pectorals or ventrals; it is impossible to assert posi- 
1 Geol. Survey Illinois, vol. 6, p. 448 et seg. ?Ibid., vol. 6, pls.18, 19. Ibid, p. 454, pl. 19, figs. 1-3. 
