42 MR. W. K. PARKER ON THE STRUCTURE AND 



p. 40G), much like the large It. kexadactyla, but always remauis small : its skull 

 (Plate 10, figs. 7-10) does not suggest a specific identity with that type, of which it 

 might be mistaken to be the young'. A young individual of the large kind of this 

 size would have a very similar skull, yet there is no reason to suppose that the two 

 are identical ; nevertheless, this is an arrested form. 



Besides the external characters by which this kind differs from the last — R. gracilis — 

 the skull itself shows a difference of character, although on the whole the variation seen 

 is very much what would be found between an adult and a young of this somewhat 

 larger species. 



The occipito-otic regions (Plate 10, figs. 7, 8) are here less solid tha.n in E. (jracilis 

 and much less ossified, for much of the horizontal, and nearly all the posterior canals 

 (fig. 7, pr.o., e.o.) are uncovered by bone, so that the four " centres " are distinct, even 

 above. The cranial " barge " does not widen out so much towards the postorbital 

 region, and the gii'dle-bone (eth.) is of less extent. 



In front there is a " prenasal rostrum," but it is shorter, and the pro-rhinals are 

 shoi-ter and broader ; among the outworks of the nose, viz. : the upper labials {u.l^.it.l-.) 

 we find a small sigmoid "septo-maxillary" (s.m.x.). The other more constant, investing 

 bones are very similar, but the parietal region is narrower, and the parasphenoid {pa.s) 

 is less elegant. The squamosal (sq.) covers very little of the " tegmen tympani ;" the 

 " annulus " (a.ti/.) is even larger, and a perfect ring ; the quadrato-jugal scarcely affects 

 the quadrate at all, and the hyoid cornu {c.h>/.) keeps free, above. The stapes 

 (fig. 10, St.) is less, and the -'columella" (Plate 6, fig. 12, and Plate 10, fig. 10) is very 

 inferior m development to that of It. gracilis, yet its inter-stapedial segment (i.st.) can 

 be seen to be distinct from the medio-stapedial [m.st.). But the form of the main 

 rod is more simple and undeveloped ; the extra-stapedial [e.st.) is a mere rounded, 

 soft end of the rod, and there is no " supra-stapedial " band. 



The mandible is ([uite normal, but shows the crest on the dentary near the chin 

 (Plate 6, fig. n, d.). 



The hyo-branchial apparatus (Plate 10, fig. 9) is also quite typical, it shows, how- 

 ever, some difference in this, that the lobes which grow out from the cerato-hyal and 

 the base, are smaller. 



There are some curious points of difference between the skull of this little Oriental 

 Froo- and that of a young Hana temporaria of the same size ; the following are 

 noticeable : — 



1. A definite prenasal rostrum. 



2. Smaller septo-maxillaries. 



3. A more arrested squamosal. 



4. A crested " dentary." 



5. An arrested columella, without an ascending part, and with the distal part a 

 mere bud. 



Minute, but measurable, differences are to be found between species and species, 



