8G MR. W. K. PARKER ON THE STRUCTURE AND 



outwards, finishing the Eustachian rim (e'^), and from thence passes downwards and 

 forwards to the basal plate, which difters but little from the norma.""' 



Second genus. Gomj^hohates. 

 18. Gomphdbates {Leiuperus). ? sp, — Adult (?) ; 10 lines long. River Plate. 



This small Frog was, apparently, adult, and yet so arrested ui 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 breadtli 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 [f.m.). The auditory capsules are like 

 those of a young Common Frog in general condition, but they have a i:)eculiar character 

 seen in metamorphosing larvae of Pscudis (Plate 11), viz. : a floor to the tympanic 

 cavity pi'ojecting beyond the fenestra ovalis and stapes (fig. 1, at.). The teginen 

 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 httle 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 hy a jiat facet with the 

 ethmo-palatine {c.])a.), 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 Pseudts differs from the "norma" in many things, viz. : — 



1. Intense ossification of endocranivim. 



2. Sub-pedunculato occipital condyles. 



3. No secondary fontanclles. 



4. A prcnasal rostrum. 



5. Solid dentigerous lobe to vomers. 



6. No proximal segment or distal process to columella. 



7. Hind edge of parasphcnoid eniarginate. 



8. Extreme solidity of pedicles. 



9. Ossification of quadrate region. 



