188 PROP. W. K. PAEKER ON THE STRUCTURE AND 



bones for half their length ; and two fifths of the frontals are between the fore half of 

 the parietals. 



They are overlapped by two pairs of bones in front (j>x, et.n) ; yet their fore part, 

 narrowing in, reaches nearly to the point of the nasal sacs. 



These two pairs of bones, the frontals and parietals, form a shallow, sloping, but a 

 scarcely crested roof; the latter rise most in the fore part of the sagittal suture 

 (PI. XXXIX. fig. 1,2J). 



The median suture is continuous from the occipital ring to the premaxillary edge ; 

 two submesial bones finish this suture in front ; they are two thirds the size of the 

 frontals, are oblong, have rounded ends in front, and are styliform behind, where 

 they are intercalated with the frontals, and repeat the imbrication of those bones 

 on and between the parietals. 



The right bone is the larger of the two. In the middle of their suture there is a 

 small round passage, like the " parietal fontanelle " of a Lizard ; this is the " middle 

 nasal passage " (m. n. p). These bones lie inside the nasal processes of the premaxillaries 

 {j)x), and far from the rudimentary nasal roof {iia) ; they are not the nasals, which I 

 do not find in this species, but correspond to the two long, narrow, superethmoidal 

 splints of the Pike (Huxley, Elem. Comp. Anat. p. 168, fig. 69, 3). Similar bones acquire 

 an immense length in Lepidosteus. They are represented by a single piece in a large 

 number of types above and below the Urodeles (e. g. Clarias, Salmo, Iguana, &c.), and 

 are simply " dermo-ethmoids." 



Embracing these bones, we see another pair of bones more than half as large, 

 hooking round and close to their foremost two thirds, and appearing as small elliptical 

 plates, which are covered with horn, and have no teeth, on the lower surface 

 (PI. XXXVIII. figs. 5, 6, ps) ; these are the premaxillaries — symmetrical, but feebly 

 developed bones. These bones meet in front, bending round the superethmoidal 

 plates ; and this front part, with its fellow, forms an arcuate tract below. The max- 

 illaries (mx) are small seed-like centres opposite the middle of the premaxillaries. 



Another lateral bone is seen behind; this is the squamosal (sq), a falciform bone 

 with its point behind and above clamping the epiotic " horn," and discoid below, where 

 it has taken on the form of the suspensorium, the articular region of which is dilated like 

 a snail's foot. This is a very simple subcutaneous scale, very much like a preopercular, 

 but bent in the opposite direction, and modified by the curious distal dilatation ; it has 

 no posterior process like that seen in the Menopome (PL XXXVIII. fig. 1, sq, and 

 PL XXXIX. figs. 5, 6, sq). 



Beneath, the endocranium is almost completely floored by the parasphenoid (pa.s) ; 

 here this bone attains almost its greatest relative size, but it confines itself to the basis 

 cranii ; it is longer, relatively, in the Sturgeon, where it runs under the fore part of 

 the spine. 



In the lower view (PL XXXVIII. fig. 6, pa.s) this bone is seen to be a large slab, 



