488 
MR. W. K. PARKER ON THE DEVELOPMENT 
temporal scute over the same region ; the “ squamosal/’ a bone only, exceptionally 
present in the Teleostei among the Siluroids. 
The post-pituitary band of cartilage, a feeble promise of the solid post-clinoid wall 
of the “ Amniota,” is now complete. Some things characterising this type are now 
well seen, namely, the small lateral ethmoidal bone in the thin, closing-in, skull wall, 
without any prefrontal (ali-ethmoidal) wing, the double “ articular” centre, and the 
huge coronoid crest to the articulo-Meckelian rod; these two latter characters are also 
seen in Amia calva, as shown by Professor Bridge. 
The very small size of the preoperculars, the form and size of the interop ere ular, 
which here so strongly resembles the preopercular of the Teleostei, are very noticeable 
in this skull, as also the long chain of bones interspersed between the “os mystaceum” 
or edentulous maxillary and the premaxillary. 
The adult condition of the skull in Polypterus and Amia (Traquair, Jour, of Anat. 
and Phys., vol. 5, plate 6, pp. 166-182; and Bridge, ibid., vol. 9, plate 23, pp. 605- 
622) presents so many things, both in likeness and contrast, that they must he noticed 
in conclusion. 
In Polypterus, as in Lepidosteus, the four fontanelles are permanently open; the 
basioccipital projects far beyond the oblique foramen magnum, and the occipital bone 
is single, made up evidently of a basal and two lateral pieces, without a supraoccipital; 
then there are no pterotics, and the olfactory capsules are sub-terminal. But in this 
type there are no epiotics distinct from the opisthotics. 
There is a large sphenotic hone, right and left, which takes up the antero-posterior 
sphenoidal regions and part of the lateral ethmoidal, besides which there is a pair ol 
lateral ethmoidals which project outwards, and an ethmo-septal hone in front. 
The metapterygoid in Polypterus is far from the skull, in which there are no basi- 
pterygoid processes; the palatine is a small ectosteal bone; the hyomandibular has 
only one centre; and the preopercular is continuous with the squamosal, as in the 
Amphibia; there is no interopercular. 
But Amia calva has a skull which comes much nearer to that of Lepidosteus in 
several respects, but the lateral and inferior fontanelles are filled in, in this solid skull, 
which comes nearer that of the Physostomous Teleosteans. 
The basioccipital projects behind the oblique foramen magnum; there is no supra¬ 
occipital, nor any pterotics, and the epiotics are distinct from the opisthotics. 
It has a pair of bones wdiich are not seen in Lepidosteus, namely, the orbito- 
sphenoids; and its so-called prefrontals or lateral ethmoids project, as in the Teleostei. 
It has a distinct pedicle to the suspensorium, capped with cartilage, but not forming a 
definite joint with any distinct basipterygoid. 
Its palatine cartilage is ossified both endosteally and ectosteally; and the wdiole 
palato-pterygoid is almost Teleostean in its solidity. 
There is a large coronoid crest, and there are two articular bones on each side, as 
in Lepidosteus. There is a cartilaginous inter-hyal, articulated between a distinct 
