202 mi. W. K. PARKER ON THE STRUCTURE AND 



segmented otlj and is also very narrow ; it soon dilates into a sub-orbicular convex 

 extra-stapedial (e.st.), which gives off a supra-stapedial band (s.st.) that Ls confluent 

 above. 



The labials {u.l\u.l~.), septo-maxillaries (s.mx.), and the marginal hones (px.,mx., q.j.) 

 are all like those of the hist kind, but smoother and less sohd in this yoimg specimen. 

 The ear-shaped top of the squamosal (sq.) does not reach the roof-bones, and is less 

 broad in its postorbital region. The roof-bones {f-p-) are already ancliylosed to the 

 endocranium behind ; the fronto-nasal suture is more triangidar. The cerato-hyal 

 (Plate 38, fig. G, ch;/.) is broad in the middle without any sudden enlargement; the 

 basal plate (b.h.hr.) is narrower than in tlie last kind ; the anterior lobes are broader, 

 and the right hind lobe is ear-shaped also. 



The differences here noticed are partly due to age, but some of the modifications 

 would be found in the skull of an old uidividual ; it is more liauinc, having a separate 

 inter-stapedial piece. 



57. Bufo agua.— Old female, 6-5 inches; young do., 5 inches long. South America. 



This lai-ge kind has a skull which is the Bii/bniiie counterpart of that of the Bull- 

 frog [Rana piju'ens) ; they are the largest of the Order, or have scarcely any rivals, and 

 in both the skull has much that is archaic or generalised. In the great Frog the skull 

 is smooth and neat, and very narrow in the interorbiLal region (Plate 8) ; here the 

 roughness and strength, and the breadth of the mid skull, are all exaggerated : the 

 one is a caricature, so to speak, of a Frog's skull, and the other of a Toad's. 



In this (Plate 36), as in the last, the length is only three-fourths of the breadth ; 

 here the condyles of the quadrate go as far back as the root of the occipital condyles, 

 but they fall short, very much, of what is seen in the larger Frogs. 



The ossification of the endocranium is much greater than what we have seen in 

 the Ethiopian B. pantherinus; and here, with no pretence to the sub-Ganoid condition 

 such as is seen in some Frogs, the investing bones are very extensive, solid, and 

 coarse. 



There is a great approach here to the triangular form in tlie general outline ; this 

 will be seen stLU more in the species yet to be described ; the hinder margm shows 

 all the projections to be almost flush with an imaginary transverse line drawn across 

 the skull behind ; the occipital condyles project beyond, the quadrate condyles reach, 

 and the epiotic eumiences just come short of, sucli a Une. The occipital condyles 

 {oc.c.) are sub-oval, *w^;ero-posterior, they are of moderate size, and are separated by a 

 crescentic notch larger than themselves. The whole hind skull is one mass of bone 

 up to the covered tegmen tympani ; in a younger individual (fig. 4) this part is 

 largely cartilaginous ; the ossification reaches in front to the optic fenestrse (II.). Only 

 one-fourth of the interorbital region is unossified, and only the front half of the nasal ; 

 the girdle-bone takes up all its own region and half of the nasal and orbito-sphenoidal. 



