% 
PLEURACANTHIBiE. 
15 
hyomandibular is slender, as in Notidanus and the later Hybodonts. 
The cartilages are permeated throughout by centres of calcification; 
but, as already remarked by Garman \ Cope’s determination of dis¬ 
tinct tracts as corresponding to several “ elements ” 1 2 must be 
regarded as very doubtful. The following is the synonymy of the 
two species :— 
Didymodus texensis , E. D. Cope, Trans. Amer. Phil. Soc. vol. xvi. 
(1887), p. 285; Didymodus , Cope, Amer. Nat. 1884, p. 412, 
and D. compressus (Newberry), Proc. Amer. Phil. Soc. 1884, 
p. 573; Diacranodus compressus, S. Garman, Bull. Mus. 
Comp. Zool. Harvard Coll. vol. xii. no. 1 (1885), p. 
Didymodus platypternus, E. D. Cope, Proc. Amer. Phil. Soc. 
1884, p. 590, and Amer. Nat. 1884, p. 412 : Diacranodus _ 
platypternus , Garman, loc. cit. p. 30. 
If truly generically distinct from Pleuracanthus, it will be pre¬ 
ferable to adopt the name Diacranodus , the term Didymodon having 
already been occupied for a mammal (Blake, Geologist, vol. vi. 
1863, p. 8). 
Teeth identical with those named Diplodus also occur in the 
Keuper of Somersetshire (Moore Collection, Bath Museum), 
Genus CHONDRENCHEZjYS, Traquair. 
[Geol. Mag. Dec. 3, vol. v. 1888, p. 103.] 
This imperfectly known and remarkable genus is provisionally 
associated with the Pleuracanthidse, on account of the striking 
resemblance of its axial skeleton to that of the Permian iishes 
described above as Pleuracanthus decheni. The body is very similar 
in form; there is the same long dorsal fin and pointed tail; the 
calcifications in the sheath of the notochord appear to agree in every 
particular ; and the cartilaginous apophyses have a similar “ beaded ” 
appearance. In Cliondrenchelys , however, there is no dorsal spine; 
the interneural supports of the dorsal fin-rays seem to be in a 
single series, instead of in two ; and no paired fins are distinguish¬ 
able in known specimens, though the well-developed character of 
the pectoral girdle is suggestive of this circumstance being due to 
accident in preservation. The snout is pointed, and Dr. Traquair 
describes a “ spicular-looking body lying longitudinally in the middle 
of the head,” which may possibly be a parasphenoid membrane- 
bone. 
1 Bull. Mus. Corap. Zool. Harvard Coll. vol. xii. no. 1, p. 29. 
2 Proc. Amer. Phil. Soc. 1884, pp. 573-577. 
