DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 89 



1. The small size of the ex-occipita,ls and prootics. 



2. No girdle-bone. 



3. The fontanelle single and largely uncovered. 



4. The evident outlines of the elements composing the nasal i-egion. 



5. The presence of a prenasal rostrum. 



G. The articulation of the ethmo-palatines with the ethmoid above. 



7. The rudimentary condition of the annulus and columella. 



8. The arrested state of the mandible and simple condition of the hyo-branchial 

 structures. 



9. The absence of teeth on the vomers. 



Third genus. Cystignathus. 

 19. (A) Cystignathus ocellatus (?). — First larva. Brazils.* 



First larva ; 2\ inches long ; tail 1 h inch ; hind legs not visible. 



This is the most immature of the Batrachian larvEe of which I have as yet given 

 illustrations in this memoir ; I have already referred the reader to much eai'lier stages, 

 figured and described in my published papers. 



These skulls are relatively very solid, and what strikes the eye at once is their 

 oblong form and the straightness and width of the cornua trabeculse. The chondro- 

 cranium (Plate 17, figs. 1, 2) is quite complete, and it has passed from the simple 

 primary condition by having had three osseous tracts applied to its surface {f.p.,pa.s.). 



Except for the projecting cornua and labials, the skull up to the quacbate condyles 

 (g.c.) is very evenly oblong, and only one-tenth longer than broad. The occipital con- 

 dyles (oc.c.) project but little beyond the auditory swellings; the halves of the basal 

 plate are separated by a considerable notochord (nc), and the cartilage w-hich \mites 

 the basal plates with the periotic capsules is young and crowded with corpuscles. 



The tegmen cranii, both fore and aft, is also made of young cartilage, and its 

 boundaries are traceable ; it leaves one large fontanelle {fo.), which is pyriform in 

 outhne, with the stalk behind. Up to the middle of the internal nostrils (/.?i.) the 

 intertrabecular plate has conjugated the trabeculte {ti\) ; from thence the massive 

 cornua (ctr.) diverge gentl3% Behind, the canals of the ear (fig. 1, a.s.c, h.s.c, jxs.c.) 



* These were taken with the species here named, and presurmMij hclontpng to it, from Rodsio (a tributary 

 of Kio des Macacos) above the Falls, Brazils, May, 1805 ; they are the gift of Prof. A. Aoassiz. I shall 

 treat of these as belonging to the type named, with the above explanation, as also the skull of another, 

 much smaller larva, with no title, but only the locality from which it was taken, namely, Lake 

 Jannarg, Manaoo, Brazils. Whichever genus the larger Tadpoles Iwlong to, to that also the little larva 

 belongs ; these two species have larval skulls very distinct from what is seen in Raiia, Calyptocephalw, 

 Cycloihitmphtie, the Hylidse, or the species of Ihi/o ; they arc most like those of the earlier stages of 

 Psemlis. Merely as a study of a variety of the larval Batrachian skull they are very valuable; and I trust 

 that some friend will verify their title for mc, and if there be any ciTor, correct it. 



MDCCCLXXXI. N 



