
OF TRISTICHOPTERUS ALATUS. 389 
of the maxillary teeth cut in transverse section. But a still clearer illustration 
of the structure and arrangement of the teeth is seen in another specimen (fig. 
7), being a horizontal section of a portion of a jaw in a piece of grey limestone 
from the same locality, and which was found naturally polished by the waves. 
The internal structure of the teeth here exhibited corresponds so closely with 
that seen in the last-mentioned unquestionable specimen of 7ristichopterus, that 
we are tolerably well justified in assuming the specimen to belong to the same 
species.* Here the bases (A. A.) of two of the larger teeth are seen in section, 
each having the empty socket of another beside it, and in addition we find no less 
than 26 smaller teeth cut through, the latter becoming gradually smaller towards 
the middle of the interval between two larger ones. In both of those specimens 
the transverse sections of the bases of the larger teeth measure from +}, to 4 
inch in diameter; in some the section is quite round, in others slightly oval. A 
small central pulp cavity is shown with the dentine around it arranged in a few 
simple plications, most of which, though not all, reach the central cavity; in this 
manner the pulp cavity appears in the section to send out a number of narrow 
radiating prolongations towards the periphery, a few of which are seen to bifur- 
cate. Further up in the body of the tooth the dentinal folds become shorter, 
and the pulp cavity proportionally larger till towards the apex the latter has 
become perfectly simple. The pulp cavities of the smaller teeth appear to be 
perfectly simple throughout. 
Whether or not Tristichopterus was possessed of palatal teeth is not dis- 
coverable from any of the specimens under description. 
The Shoulder-Girdle and Paired Fins.—None of the specimens show very 
distinctly the upper attachment of the shoulder-girdle to the skull, or the form 
of the supra-claviculars. In one, evident traces are seen of a powerful second 
supra-clavicular (s. cl, fig. 10) extending downwards and backwards to articulate 
with the next or clavicular element, but too crushed and indistinct for special 
description. The clavicle (cl, figs. 1, 6, 9, and 10) is well marked in all; it isa 
stout, broad, oblong plate, expanded and produced a little forwards below ; its 
outer surface is marked with the characteristic ridged-granular ornament, while 
its smooth internal aspect shows three peculiar rounded impressions, probably 
for the attachment of the coraco-scapular elements of the base of the pectoral 
fn. Articulated with the front of the lower end of the clavicle is another smaller 
plate (2.cl), the interclavicular of PARKER,—the “ accessorisches Clavicularstiick” 
of GEGENBAUR. 
The pectoral fin itself (Pl. XXXII. figs. 9 and 10) is large, obovately fan- 
shaped, terminally rounded, and consists of very numerous slender rays, attached 
* Since the above lines have been in type, the Museum has acquired from Mr Peach an addi- 
tional and nearly perfect specimen of Tristichopterus, in which, near the front of the head, the base of 
one of the large teeth is seen broken, or cut, across in transverse section. The transverse section of 
this tooth is $ inch in diameter, and displays a structure absolutely identical with that described above, 
