OF THE SKULL IN' LEPIDOSTEUS OSSEUS. 
445 
Traqtjair, Dr. E. H. 
1. “ On the Cranial Osteology of Polypterus.” Jour, of Anat. and Phys., vol. v., 
pp. 166-182; plate 6. 
2. “ On the Ganoid Fishes of the British Carboniferous Formation.” Trans. 
Palaeont. Soc., 1877 (Part I. : Palaeoniscidae), pp. 1-60 ; plates 1-7. 
3. “ On the Structure and Affinities of the Platysomidse.” Trans. Eoy. Soc. 
Edinb., vol. xxix., pp. 343-391 ; plates 3-6. 
Wiedersheim:, Dr. Eobert. ( Das Kopfskelet der Urodelen/ Leipzig : 1877. 
The skull of the adult Lepidosteus. 
This skull, which belongs to the long-beaked variety, is more than a foot long, and 
the foremost two-thirds of its length belongs to the “ rostrum,” which is gradually 
attenuated from behind forwards, and then dilates gently at the fore end. The olfac¬ 
tory sacs are very small, and instead of being placed close in front of the antorbital 
region, are carried to the end of the snout, and have on each side a pair of holes 
bounded by small bony plates. The orbits are a little above half an inch across, and 
they are bounded by a perfect “ circumorbital ” series. The auditory capsules are 
impacted into the walls of the hind skull, which at the sides is only about one- 
twentieth the length of the head. The occipital condyle is behind the skull; the 
condyles of the quadrate are in front of the orbits. There is no fontanelle in the 
perfect skull—that space is entirely covered by large ganoid scutes. 
A. On the superficial plates or “ scutes .” 
Beginning at the occipital roof, we find the hind skull covered with two large plates 
that represent the parietals; here, at once, we see how variable these scutes are, 
which answer to much more than the investing bones in the higher types, for there is, 
on the left side (in my specimen), an irregularly four-sided “dermo-occipital,” the inner 
edge of which passes over the mid-line a little. Thus the right parietal is much 
larger than the left. Outside each parietal there is a somewhat smaller scute—the 
squamosal; this bone finishes the roof. The two or three small, irregular scutes behind 
the squamosal are u post-temporals,” and serve as fixing-points to the clavicular series 
of the shoulder-girdle ; they are post-cranial. 
Outside the hinder part of the squamosal there are two smallish additional 
“temporal” scutes, wedged in above the “opercular.” 
In front of the parietals and squamosals we see the frontals; they interdigitate by 
large, sharp, sutural teeth, with those bones, and then run on over the orbital region, 
and over the hinder two-fifths of the rostrum. They are elegantly narrow-waisted 
(taken together) in the orbital region, and they contract into sharp styles in front, 
where they embrace the next pair. 
