AFFINITIES OF RAN A SUBSIGILLATA. 2.5 



Its most salient characters are : — 



1. The prolonged squamoso-maxillary suture, a feature which 



it shares with 7i'. acUpersa alone. (See text-figs. 1 a, c ; 

 2 a, h, G, e.) 



2. The fourth pterygoid process, which it appears to share 



with R. ktihlii alone, although a faint indication of this 

 pi'ocess is sometimes met with in B. ads2}ersa. (See text- 

 figs. lh,c; 2 d.) 



3. The marked overlapping of some of the membrane-bones, 



the most important of which are : — 



a. The interior branch of the pterygoid on the transverse 

 limb of the parasphenoid ; an overlap only otherwise 

 found in R. adspersa. 



h. The interior limb of the squamosal on tlie prootic, as in 

 R. adsjyersa, R. grunniens, R. macrodon, etc. 



c. The nasals and fronto-parietals almost entirely obscuring 

 the ethmoid, as in R. adspersa and R. tigrina. (Text- 

 figs. 1 and 2.) 



4. The slight pitting of the nasals, dorsal plane of the fronto- 



parietals, zygomatic processes of the squamosals, and the 

 ma.xill8e ; a character carried to excess in R. adspersa, in 

 the adult of which these bones are covered with granular 

 asperities. (Text-figs. 1 a, c ; 2 6, c, e.) 



As regards the squamoso-maxillaiy suture and the pterygoid 

 overlap, it is an extraordinary thing that, whereas in no other 

 species of the genus Rana are these chai'acters exhibited even in 

 old age, in R. subsigiUata and 7^. adspersa they are well marked 

 even in specimens imder a year old, in which the frontals are 

 still separated from the parietals (see text-fig. 2 a). This 

 seems to me to greatly enhance the importance of these features, 

 proving them to be no recent modification, and to isolate 

 completely these two species among all others of the genus. 



It is thus clear that the two species are closely related, a fact 

 which seems conclusively proved by the development of the skull 

 in the young R. adsjjersa. 



Specimens of this frog at about one year of age (text-fig. 2 a) 

 resemble in every cranial character the rather older young of 

 R. subsigiUata. They have the frontals yet separated from the 

 parietals by oblique sutures ; the sagittal suture is complete, and 

 a moderate portion of ethmoid is exposed above. At this stage 

 the skull shows no rugosities. At the age of about two years 

 (text-fig. 2 b) the skull shows signs of pittings, and the fronto- 

 parietals close in and expose slightly less of the ethmoid. At 

 the age of about three years (text-fig. 2 c, d) the skull con- 

 forms so exactly to that of R. sid)sigillata that (except for the 

 foiirth pterygoid process) to describe it would be to recapitulate 

 the greater part of this paper. It has, however, slightly longer 

 and more closely-set pra?maxillary processes, and consequently a 

 more pointed nasal roof, less triangular nasals, less developed 

 extrastapedials, and a less prominent quadrate. 



