TIIK I'.ATRACIIIA OF XORTII AMKUICA. 



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of l.S' , \vlii(;h jiiv witlioiil j;ills, it is ;i very minute tubercle on tiie 



outer inetiitarsiis. In ■'■. '■'tie eailier stiige it (t.iii not but be wantinj^, 

 tlioiijjli this I liiive not seen, and I have little doubt that it is then a 

 llernidaetylium, unless, indeed, the parietal bones be not ossified. 



Another fu'tal condition rendered pernianent is seen in the generic 

 character of the <;enus (Hdipus, whi(!h dilfers from Spelerpes solely in 

 the f«etal non-separation of the dijifits which continues even after the 

 bones of the diffits have been developed. In the larva of Sp. ruber the 

 digits are early entirely distinct, so that so far as this species is con- 

 cerned (Edipus i)resents an inc.ract parallelism, but they are also 

 nu)redistin(!t than in the mature ISpclerpeH beJlii, where, as might besup- 

 I)osed, the fo'tal union is delayed to maturity in other respects, as ip a 

 speirinu'U from Orizaba, INIexico, of l(!.o lines in length. There the union 

 is about as extensive as in (Etlipm iiiorio. In the young of Tliorius 

 peniuttttluN, the digits are not distinguished in specimens of .GO of the 

 full size, and otherwise entirely mature. In the adult they are distinct 

 for half their length. The digits in the young larva of Gyrinnphilus 

 porphi/ritiruH are as distinct as in those of Spelerjtcs rubra. In one exam- 

 l)le 1 find the simple foot of earlier stages retained, resembling exactly 

 that of (Kdipus, excepting that there are emarginations for but three 

 toes instead of five, (lenera which have no ])remaxillary fontanelle 

 at maturity have it in the larval stage. Finally, closely allied genera, 

 whi<!h only dilfer in the degrees of ossi/ication of the parietal and pala 

 tine bones, represent simply the relation between undeveloped an<l 

 developed conditions of the same form. 



The relations of the genera maybe expressed as follows: Those of 

 the first or Plethodontine se(!tion are related to those of the second or 

 Spelerpine by an incraet parallelism, excepting Autodax, whose pecul- 

 iarities exclude it from the comparison. Those in ea(!h section differing 

 in the union or separation of the premaxillary bones are ndated in 

 the same way to each otiier. The nearly allied genera in the IMethodon- 

 tine groui) are llernidaetylium and Plethodon, and liatrachoseps and 

 St<'re()chilus. In the first case we have only inexact parallelism, because 

 while Plethodon lias the four digits of llemida(!tylium, its parietal 

 bones are unossified, tliough an acceleration of development in these 

 respects would render the relations one of c.raef p((rallelis))i. This is 

 apparently the relation between l>atrachosei)s and Stereochilus, Ww 

 with the fcetal digits of the latter the former preserves also its fcetal 

 cranium. It only renniins to ascertain whether Stereochilus loses its 

 branchiae before or after aecpiiring the normal number of digits. From 

 the very small size of one at least of these the fcn-nu'rcase seems pro!) 

 able, but I have not yet been able to prove it by direct observation. 

 Should it be so, we would have a <!ase of crnet jmrrt//f/j.v»i. 



In the Spelerpine group the relation between (leotriton and Gyri- 

 uophilus is again one of inentet parailelism, since when the digits of 

 the latter are only separated at the extremities, as in the former, the 



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