86 
MR. W. K. PARKER OK THE STRUCTURE AND 
outwards, finishing the Eustachian rim ( eu .), and from thence passes downwards and 
forwards to the basal plate, which differs but little from the norma.'" 
Second genus, Gomphobates. 
18. Gomphobates ( Leiuperus ).-? sp.—Adult (?) ; 10 lines long. River Plate. 
This small Frog was, apparently, adult, and yet so arrested in certain respects, as 
well as so very small, that it answered to the young of the Common species taken about 
the end of July. The chondrocranium of this kind is so very instructive that the 
figures are only made to show this, and certain of the bony plates attached to it. 
The general outline of the skull (Plate 13, figs. 1, 2) is semi-oval and the breadth is 
a little more than the length. The notochord (nc.) is still large, and lies upon the 
united moieties of the basal plate. The occipital condyles (oc.c.) are normal; and 
the emargination between them moderate; but the roof has a much larger crescentic 
notch than usual over the foramen magnum ( fm .). The auditory capsules are like 
those of a young Common Frog in general condition, but they have a peculiar character 
seen in metamorphosing larvse of Pseudis (Plate 11), viz. : a floor to the tympanic 
cavity projecting beyond the fenestra ovalis and stapes (fig. 1, st.). The tegmen 
tympani is of very small extent, and only exists in front. 
The 9th and 10th nerves (IX., X.) are surrounded by a very limited ex-occipital (e.o.), 
and the prootic ( pr.o .) only forms an oval patch behind the foramen ovale (V.); this is 
entirely on the lower aspect of the skull; the ex-occipitals just reach the upper surface 
between the ear sac and the occipital arch. 
The interorbital region is rather broad, a little bulging, and considerably narrower in 
front than behind; it is well walled in with cartilage, the optic fenestra (II.) being of 
the average size ; and the top wall grows over on to the roof for some distance, leaving 
one oval fontanelle (fo.) about half as large as the whole roof. The anterior part of the 
tegmen cranii is well developed, and the hind part is nearly as long as the fontanelle. 
The ethmoidal wings end abruptly above, and articulate by a fiat facet with the 
ethmo-palatine ( e.pa .), but are quite continuous with it below; there is no rudiment 
even of the girdle-bone. 
The figures given of the upper and lower aspects of the ethmo-nasal region, might 
* The skull of the adult Pseudis differs from the “ norma ” in many things, viz.:— 
1. Intense ossification of endocranium. 
2. Sub-pedunculate occipital condyles. 
3. No secondary fontanelles. 
4. A prenasal rostrum. 
5. Solid dentigerous lobe to vomers. 
6. No proximal segment or distal process to columella. 
7. Hind edge of parasphenoid emarginate. 
8. Extreme solidity of pedicles. 
9. Ossification of quadrate region. 
