158 UTl. W. K. PARKP:R ON THE STRUCTURE AND 



10. The unique ossification of tlie large basal plate, and the crested growths of the 

 thyro-hyals. 



In the next kind of dwarf " Polypedatid," — a smaller species than the last and from 

 another region, — the signs of arrest are more numeT'ous, and some of these stoppages 

 must have taken place early in the larval stage ; moreover there is but little sign of 

 compensating growth, in over-ossification and the like, such as is seen in the one just 

 described. 



42. Rappia {Hijperolius) hicolor. — Adult female ; f inch long. Dog-trap Road, 

 Paramatta, Australia. 



This is a rather long skull, for the length and gi'eatest breadth are equal. The 

 quadrate condyles (Plate 19, figs. 6, 7, q.c.) end opposite the middle of the medio- 

 stapedial {m.st.). The mid skull is one-third longer than the other two regions, which 

 are equal to each other in tliis respect ; they are both moderately broad, but tlie mid 

 skull is very broad. 



The interauditory region is nearly as wide as the interorbital, and this latter 

 increases in width forwards. The " tegmen cranii " is' very slight in front, largely 

 covers the hind brain, and there is left a fontanelle {fo.) which is evenly egg-shaped, 

 and has its wide end in front. 



There is a very narrow band of cartilage bounding the fontanelle on each side, but 

 this is not continued downwards into the toall, wliich is membranous, except for a short 

 distance at each end. 



There are two rather large secondary fontanelles in the extensive interauditory roof. 



The occipital condyles [oc.c.) are small, sub-reniform, and postero-inferior ; they are 

 separated by a straight basal tract equal to both in width. The basal cartilage is equal 

 to one condyle in width, and the upper or sujoraoccipital cartilage is as wide as the 

 intercondyloid space. 



The four bones {pr.o., e.o.) are larger than in the last; the ex-occipitals reach the 

 fenestra ovahs below, and are wider above ; the prootics cover the anterior canal (a.s.c), 

 nearly, floor its "ampulla" below, and go round, but not in front of, the foramen 

 ovale (v.). There is a moderate tegmen tympani (fig. G), and the canals and vestibule 

 bulge out above and below [h.s.c, a.s.c, p.s.c, vh.). 



The tegmen cranii becomes a narrow band directly it passes into the interorbital 

 region, for the trabeculee {tr.) have not enlarged, relatively, since the legs of the 

 Tadpole began to bud out, only the intertrabecular tract of cartilage was added. 



The optic foramen (II.) is lai-ge, but the optic fenestra (or fontanelle, o.fo.), which 

 is large in several types of small Australian Anura, here occupies nearly all the orbital 

 region; it is one-third the length of the skull. The bulging floor of the skull widens 

 towards the ethmoidal region, and then, behind the true nasal region, there is a com- 

 plete girdle for a sl)ort distance — not a complete hony girdle, however, yet there are 



