NKW AND IJTTl.K KNOWN PALEOZOIC 
li.. H-. i" speeiali/ation 
of n ,...M,.«.-| ....l««I.T TIm* writn- that this tendency tn compress the 
in the anterior fin nnufrin mu.l.l only occur when the hue of the 
l««,U i*«. ..till iniU-d.hHl ill the IhmIv wall.— and would trace this conclusion still 
further to m-eoiinl for the aiioiiinlous liii spines oC the Acanthodians. In Parexus, 
r..r exuiii|.|e. it Mould MH-III .|iiite clear that the broad fin spine is structurally corn- 
|..lln•l. aii.l limy Me|| n-pn-si-iil the fusion <.f the radials in the anterior fin 
iiinr^'iii 
••III the ventral of OnM*srla(hc is repivsented the most primitive condition 
Inlherto kiioMii in the onto^reiiy of the paiivil limbs. The fin is still outwardly a 
ImmIv ileriii folil. thrice as loiitr ns broad, hlmiterl anteriorly where the radials are 
laviniiiii;; to U» chiHicnil ; the basal siip|M)rts. in number scarcely less than the aji- 
|s-nde<l niiliiiU. are still iitiriisiMl. although the pna-e.ss of concentration anteriorly is 
clearly lo In* marked " 
To tills I have addeil.' I lint nil ol)s«*rvations on Symmorium, together with 
ihoM* of Tmi|iiair, .laekel niiil Dean, show that t he median a.\is of the archipterv- 
Kiinn is l•••| |>ropler\>'ial or iii«'s«»pt«*rvgial, hut is metapterygial. This greatly sini- 
idiliis till* eoiieepl ion of the history of the Sidnehian fin (Fig. 2), where the iiietap- 
lery jiiiiii aii|i|Nirts the greater iiiiiiiIkm- of the other segments. The Ichthyotonii are 
ihAiMii out of the phylogeiiy of the sharks, and are left in a position more likely 
lopnive niH-i'sInil to the 'relisistoinatoiis fishes: but nothing jiositive on tliis jioiiit 
• an Is* alliniMHi.' 
Kio. 8. Sri/iiio form, left 
HhmiUler-girdle; (’m, iMwttemiNiral ; 
/>', epiclavicle; D, <'lavifle: /!', ixiet- 
elHviele: ■V, scapula: Co {('(), inra- 
••iiid; ,1/' AV/. hasihu-s; A, seai)ular 
roraiuen; //.S', A’.S', liii-rays. 
tViedersliciiii. 
