CESTRACIONIID^. 
325 
an almost stellate appearance. On the right side, imme- 
diately behind the head, four or five faint transverse 
grooves in the shagreen-investment appear to mark the 
gill-slits, diminishing in size backwards. Egerton Coll. 
A fragmentary example of Paloeosphmx from the Lias of Holz- 
maden, Wiirtemberg, now in the Stuttgart JTuseum, seems to differ 
from both of the described species. Detached teeth and dorsal fin- 
spines of an undetermined species have also been discovered in the 
Rha;tic of HolweU, Frome, Somersetshire (iloore Collection, Bath 
Museum). 
Genus SYNECHODUS, A. 8. Woodward. 
[Proc. Geol. Assoc, vol. x. 1888, p. 288.] 
A genus, so far as known, scarcely differing from Pahxospinax 
except in its higher degree of specialization. The pterygo-quadrate 
cartilage in the adult is directly connected with the cranium by a 
postorbital articulation', and the vertebr® are distinctly astero- 
spondylic. Jfone of the teeth have less than two lateral denticles, 
these being generally numerous ; aU are in part delicately striated, 
and at the base of the crown the ornament is often reticulate. 
The complete dentition of one jaw of the type species of this 
genus is made known b)' a fine fossil, from the Chalk of Sussex, 
preserved in the collection of Henry Willett, Esq., Brighton Mu- 
seum. About 140 teeth are displayed in their natural relative 
positions ; and the specimen is shown, of twice the natural size, in 
the accompanying woodcut (fig. 12), with the first and second teeth 
and one of each of the alteniato succeeding series, still further en- 
larged separately. There are eleven dental series upon either ramus 
of the jaw, each of those posteriorly placed comprising as many as 
eight or nine teeth, while those near the symph 3 -si 8 have not more 
than six. There is no median sjmphj'sial row of teeth, and the 
first pair (i.) is extremely small. In the latter the principal 
coronal cusp is long and slender, its height being equal to the entire 
width of the tooth ; and there arc two small denticles in front and 
one behind. The teeth of series ri . arc nearly four times as wide 
as those of no. i., with the principal coronal cusp still very pro- 
minent and flanked in front and behind by three large denticles and 
one smaller point, of which those behind are the more widely spaced. 
The teeth of series in. are very similar to those of no. ii. ; but in 
the teeth of series iiii. and v. the principal cusp rapidly becomes 
' Proc. Zool. Soc. 188G, p. 218, pi. xx. figs. 1, 2. 
