246 PROCEEDINGS OF THE ACADEMY OP 



Nearly allied to it is the genus Osteocephalus, which differs in the normal ex- 

 ostosis of the cranium not involving the derm, as in the former. Close to this 

 is Scy topis, where the fully ossified cranium is not covered by an exostosis. 

 Nest below Scytopis is Hyla, where the upper surface of the cranium is not 

 ossified at all, but is a membranous roof over a great fontanelle. Still more 

 imperfect is Hylella,* which differs from Hyla in the absence of vomerine teeth. 

 Now the genus Trachycephalus, after losing its tail and branchiaj, possesses all 

 the characters of the genus Hylella and those of Hyla, either at or just before the 

 mature state of the latter, as the ethmoid bone is not always ossified in advance 

 of the parietals. It soon, however, becomes a Scytopis, next an Osteocephalus, 

 and finally a Trachycephalus. It belongs successively to these genera, for an 

 exhaustive anatomical examination has failed to reveal any characters by 

 which, during these stages, it could be distinguished from these genera. 



Now it would be a false comparison to say that the young of Trachycephalus 

 was identical with the genus Agalychnis, which in truth it resembles, be- 

 cause that genus is furnished with one other character, — the presence of a ver- 

 tical pupil, — and belongs to another series in consequence, which is represented 

 as yet, wiih our present imperfect knowledge, — or perhaps imperfect fauna, — 

 by three genera only. 



2. The lowest type of the near allies of our common fresh-water frogs is the 

 genus Ranula, where the prefrontal bones are narrow strips on each side the 

 ethmoid cartilage ; the ethmoid cartilage itself entirely unossified above, and 

 the vomerine teeth very few and on a small elevation. There are two species, 

 R. a f f i n i s and R. p a 1 m i p e s. The other species have the ethmoid carti- 

 lage ossiffied above, at least beneath the extremities of the frontoparietals. 



Those of the latter most like Ranula possess the same type of narrow pre- 

 frontals, separated by a broad area of cartilaginous ethmoid, and fasciculi of 

 teeth. Of this type is Rana delalandii, and probably R. porosissima 

 Steind., of the South Ethiopian region. Other species of the same type extend 

 their vomerine patches into lines ; such are R. mascariensis, R. fasci- 

 a t a, R. o x y r h y n c h u s , R. g r a y i , and other South African species. 



The prefrontals are subtriangular, and approach each other more or less in 

 the numerous species of North America and of the Regio Palasarctica, while 

 generally the vomerine teeth are in fascicles or very short series. In the 

 Ethiopian Rana f u s c i g u 1 a the prefrontals unite on the median line, roof- 

 ing over the ethmoid cartilage and reducing it, while the vomerine teeth are 

 in very sl.ort lines. 



In the species of the Pal^otropical region, Rana tigrina, R. vittigera, 

 R. cyanophlyctis, R. grunniens, R. hexadactyla, R. corruga- 

 t a, R. e h r e n b r g i i, R. g r a c i 1 i s, and the Ethiopian R. occipitalis, 

 the prefrontals not only unite solidly (the suture remaining on the median 

 line), but extend and closely fit to the fronto parietals. The vomerine series 

 have lengthened out into series. 



Now the young of the latter type of Rana (I take as an example the R. ti- 

 grina, one of the most abundant and largest of Indian frogs) presents the 

 subtriangular prefrontals neither in contact with each other or with the 

 fronto-parietals, and the vomerine series is much reduced; in fact, it belongs 

 in all respects to the PalEearctic group. I have not examined younger speci- 

 mens, but have no doubt they are like those of the Palsearctic ; the latter, then, 

 in their young stage, are precisely of the type of the Jithiopian Rana, with 

 fasciculate teeth like the young of those of the same region with teeth in se- 

 ries, since the prefrontals are still more reduced, becoming linear. Finally the 

 first stage of the Nearctic Rana, after losing the larval tail, is the genus Ra- 

 nula, having linear prefrontals, minute vomerine teeth, and the ethmoid ring 

 cartilaginous above 



These points of structure are of generic quality, but I have not regarded any 



*I refer to H. carnea m., not having Reinhardt and Lutken's type of this genus. 



[Oct. 



