
OF TRISTICHOPTERUS ALATUS. 295 
size of the exposed area of the scales, which are also mentioned as “an 
manchen Stellen des Kérpers ins Rhomboidale iibergehend,” are, however, 
very obvious marks of distinction. Yet, as to the true nature of M‘Coy’s 
Gyroptychius, there seem to be very considerable doubts. Classified by PANDER 
as one of the “ Dendrodontes,” a family afterwards merged by Professor 
Hvuxiey in the cycliferous Glyptodipterini,* and originally described by 
M‘Coy as a “Ccelacanth ’+ (¢.¢., cycliferous Crossopterygian), Gyroptychius 
was, however, placed by Sir Puitie Ecerton among the Saurodipterini,{t and 
by Huxzey in the rhombiferous section of the Glyptodipterimi.§ And it must 
be owned that, although the elliptical scale, figured by Professor M‘Coy from 
the back of Gyroptychius angustus, “very much resembles,” as Sir P. EGERTON 
says, ‘a scale of Tristichopterus,”|| yet, in the definition of the genus, its founder 
states that the scales of the flanks are “sub-rhomboidal;” and those figured 
by him from the side of G. diplopteroides are most decidedly Saurodipterine 
in form and arrangement, the surface sculpturing also very closely resembling 
the markings seen on many saurodipterine scales when divested of their 
external ganoine layer. Not having, however, yet seen the original specimens 
on which the genus was founded, I must be content, in the meanwhile, to leave 
this question as it is. 
* Dec. Geol. Survey, x. p. 23. + British Paleozoic Fossils, pp. 596-597, Plate 2, C, figs. 2, 3. 
t Qu. Journ. Geol. Soc. xvi. (1860) p. 126. § Dec. Geol. Survey, x. p. 23. 
|| bcd. p. 54, note. 
EXPLANATION OF PLATE. 
In all the figures the matrix has been omitted to save space. The same. letters refer to the same 
bones throughout. 
C.B, cranial buckler; f, frontal; p.ma, pre-maxillary; Mn, mandible; sp, splenial; op, operculum; 
s.op, sub-operculum; p.op, preeopercular cheek-plate; s.¢, supra-temporals; s.o, sub-orbitals; j, jugular 
plate; p.g, palatoquadrate arch; cl, clavicle; s.cl, supra-clavicular; 7.cl, inter-clavicular; 0, basal 
segments of archypterygium; 7, radials. 
Figure 1. Head of Tristichopterus alatus, the facial bones of the left side exhibited from the enternal 
aspect. The granulated impression of the outer upper aspect of the cranial buckler is 
shown, a good deal of the bone of its anterior division still adhering to the matrix; and 
in the upper part of the figure the preopercular plate of the right side is shown, as also 
the operculum, the latter partly in impression. 
Figure 2. Another head, seen from the right side. The preopercular plate and circumorbital bones are 
gone, the palatoquadrate apparatus being thus exposed, with a portion of the maxilla 
attached to the anterior part of its outer margin; the supra-temporals, operculum, part of 
the sub-operculum, and the cranial buckler, are seen in impression of their internal 
surfaces, part of the externally granulated bone of the latter still remaining in its posterior 
division. The mandible is rather injured along its inferior margin. 
Figure 3. Palato-quadrate apparatus detached. A portion of the edge of the maxilla, showing bases o 
numerous teeth cut transversely, is seen anteriorly and externally. 
Figure 4. Detached preopercular plate, seen from the inner aspect. 
_ Figure 5. Detached splenial of mandible (2). 
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