376 RAMSAY H. TRAQUAIR ON THE 
the arrangements did not materially differ from those in Platysomus. In this 
genus the same difficulties are also encountered, but to a less degree, as in 
many specimens from the Magnesian Limestone and Kupferschiefer, the bones 
are to a considerable extent perceptible through the scales, or are here 
and there actually exposed by the removal of patches of scales with the 
counterpart. 
Aaassiz has given a restored figure of the skeleton of Platysomus, which 
may serve as a basis for the following few remarks on the subject. It is hardly 
necessary to begin by pointing out that the osteology of the head and shoulder 
as here delineated is quite erroneous, but for that ample allowance must be 
made, considering the specimens at his disposal, and the enormous amount of 
work he executed in so short a time. More attention must be paid to the parts 
behind. Here the vertebral axis is represented as segmented into distinct 
centra by vertical dotted lines ; above, it gives off a series of short neural arches 
and spines directed obliquely upwards and backwards ; below, a corresponding 
set of hemal ones; while in the abdominal region short ribs are delineated, 
extending hardly more than + of the depth of the abdominal parietes. Above 
the neural spines, and extending from the occiput to the tail, is a lower or 
proximal set of interspinous bones (¢nterapophysaires), the most anterior of 
which are consequently placed far in advance of the dorsal fin, and they are 
also inclined downwards and backwards so as to be placed at right angles to the 
neural spines beneath; they gradually, however, alter their direction, so as 
posteriorly to become more in a direct line with the spines. The dorsal fin 
itself is represented as borne by a second or distal set of short interspinous 
bones (surapophysaires) limited in extent to the length of the fin, whose rays, 
enlarged at their proximal extremities, are articulated to the extremities of 
these supporting ossicles, with which they also correspond in number. The 
anal fin is also represented as supported by two sets of interspinous bones, the 
proximal set commencing with one very large one immediately behind the 
abdominal cavity. 
Now, in the first place, there can be little doubt that the vertebral axis of 
Platysomus was not provided with ossified centra, but consisted of a per- 
sistent notochord. It is so described by HEcKEL, who refers its condition in this 
genus to the same category as that in Paleoniscus and Colacanthus, of which 
he states that they possess in the vertebral axis “durchaus keine Spur von 
Wirbeln, oder auch nur von Halbwirbeln, Hier sind blosse Dornfortsiitze vor- 
handen, die mit einer Art von Gabeln, welche theils die Stelle der Wirbelbégen, 
theils von vereinigten untern Querfortsitzen vertreten, iiber und unter einer 
nackten Riickensaite ansitzen.”* Nor have I myself ever seen any trace of 
* “ Ueber die Wirbelsaule fossiler Ganoiden,” Sitzungsh. der Wiener Acad, 1850, Abth. 2, p. 363. 
