178 Mr. T. Stock on the Genus Tristychius. 
pulp-cavity small; its value as a specific character must, 
however, be accepted with considerable reserve. 
The seven denticles are confined to the distal fourth of the 
spine, and form a rather crowded series; they slightly increase 
in length proximally ; and their bases are fused into the walls 
of the spine. The second row (if existent) is concealed im 
the matrix. The inserted portion of the spine is not pre- 
served. 
Affinities —Giebel * figures a spine which may possibly 
come near the one just described. In the text he refers it to 
Styracodus acutus, a species and genus founded by himself 
for the reception of a very Ctenoptychius-like fossil (a 
resemblance he was quite aware of himself), In the plate, 
however, it appears as Hyhodus, along with other forms re- 
ferred to the same genus. The reference, however, is clearly 
due to carelessness in naming the figures; for it is evident 
from the text that Giebel had no concéption that the spine 
could possibly be related to the remains that he figures on the 
same plate as belonging to Hybodus. Nevertheless there is 
some ground for believing (unless all faith is refused to 
his figures) that the spine which he referred to Hybodus 
is nothing but Plewracanthust, and therefore unconnected 
with the remains in question, but that the spine named Sty- 
racodus acutus may really belong to them. This spine is 
unfortunately broken off just at the point where the denticles 
would commence if it be, as I surmise, a species of Tristychius ; 
but in other respects it conforms closely enough to the genus. 
From his figures 5 and 7 it is evident that some tolerably 
undisturbed Nelachian fragments had been discovered ; for we 
see a number of teeth associated with cuticular appendages 
upon the same slab. Separate figures of the teeth are given f, 
from which it is quite possible to gather that they bear a 
similarity (as I shall show hereafter) to teeth that occur not 
unfrequently in our own Lower Carboniferous or Calciferous 
Sandstone series, and which are associated with undoubted 
Tristychius spines. Whilst this generic affinity may be asser- 
ted pretty confidently, there is much doubt as to whether the 
species trom the two localities are the same; and therefore 
* In Germar’s ‘ Versteinerungen des Steinkohlengebirges von Wettin 
ay salad p. 71, tab, xxix. fig. 40, and reproduced in Pl. VIL figs. 2 
and 2a. 
+ Loe, cit. fig. 8; reproduced in Pl. VIL. figs. 3 and 3a. May not his 
Chilodus gracilis be a Diplodus tooth ? loe, eit. tig. 2, reproduced Plate VIL. 
figs. 4 and 4a. One-pronged Dzplodus-teeth are occasionally met with, 
whether due to fracture or not it is not easy to say. 
{ Loc. cit. fig. 5, a, b, and figs. 6 and 6a; reproduced, Pl. VIL. figs. 5, 
5a, & 6, 6a 
7 
