TIIK MATUAOIItA fH' NOltTIf AMKHIf'A. 



225 



may lu' «'X('lii.siv('I.v air ln'ciitluTs I have sIkiwii l»y tibsei'vations on a 

 spcciiiKMi in an aqnatinni wliicli, I'oi' two nioiilis, prohalily from tlui at- 

 taclvH of n«hes, had no lirancliia' at all. (Sco .lourn. Ac, I'liila., 180(}, 

 p. OS). 



In explanation of tliis tact, it may ho romarkoil that this atrophy can 

 not bu a<;roiinto*l lor on th(> .snp|)osition that it is S(>as(nial anil due to 

 the drying; np ol the a(|nati('. habitat of the sir(>ns. The tionntiies thoy 

 inliabit arehnmid, rec«'ivin<;,Mhe heaviest rain-fall of oni' ICastern States, 

 and there is no dron<;ht. The only explanation appears to me to be that 

 the present Sirens iuv t\w descendants of a terrestrial type of Hatraehia, 

 which passed thron^h a metamorphosis lik(>. other nu>mbers of their 

 class, lint that more recently tlu-y have ailopted i permanently aqnatic 

 life, and have resnmed their branchia- by reveision. 



This hypothesis is (^onlirmed by the relations of the stapes to the 

 suspensor of the lower jaw. It is not coniu'cted with the quadrate 

 cartilafje, as is the case with the I'rotiida', Cryptobranchida', Amiddn- 

 mida', and the larva- (»f salamanders, bat is distinct and is connected 

 posteriorly v/ith a stapedius muscle as in adult salamandeis.* (See 

 I'l. 1(5, ti-. .-..) 



There are but two known {jenera of this family, whicdi dilVer as fol- 

 lows : 



i>ij;ils run I ; Itriiiii'liiiil I'lMsiircs nininally lliii'c Siren. 



Dijiils (liicr ; liiuiiilii:il lissiiit'soiii' I'stnilohraiichiin. 



SlIvl'iN liinna'us. 



Anin'iiiliiti'M A<'!i(U'iiiic;c, \ii, ITCi.'i, p. lUl (tcsli' lldlliiook) : Systoma 

 NatiiiM' !•,', cd. I, p. :i71, I7(;(i: (»iM'it. l:!, cd. i, Addenda, 17<i7; iliid., 

 'riuton's I'd., l-^ti-.*, I, p. (iTl ; 'i'scliiidi. Italiai liia, p. its ; (iray Cat. 

 Itril. Mns., p. (i-*; Dnni. A I'liUr. I",rp. (icii.. ix, p. lit! ; HoiiltMij^or, 

 Cat. (irad. Ilrit. Miis., cd. ii. p. Mi, l-i+J. 



I'liaiKnihraiicliiis, pt. l,i'ii(d<ail Isis von Okcn, If^Jl, p. 'Jiid. 



Difiits four; Jaws with horny sheath; tnnyiu^ larj;e, free in front; 

 eyes distinct; external branchia' three. A patch of teeth on eac^h side 

 of the palate standinj; on tlii'cc^ plati's, wliicii an^ attached to the para- 

 sphenoid bone. Three branchial lissures on each side in the adult. 



In this ficnns tiiere are narrow (!artila,t;es on the ai>proximated ex- 

 tremities of the tiist basibranchial and the ceratohyals, in the i)osition 

 of a basihyal and hypohyals respectively. 



The transverse jjroces.ses of the vertebral are very much expanded 

 horizontally at the ba.se, but they terminate in a i)ointed ajiex. 



I ,! 



^ ;-l' 



) 



i 



If 



1951— Bull :\i- 



' AnuM-ican Xatnralist, l88-<, p. Jtll. 

 -1.J 



