NEW AND J>1TTDE KNOWN l>ADEOZ()l(’ AND MK>()Z()K’ h'ISHES. 
By E. I), (’ope. 
ELASMOBRANCHII, 
Genus SY.MMOHII AM U.)i)e., 
Hvmmokipm hbnipoume Cope, Amer. Naturalist, 189.S, p. t»9t). Plate XVI 1 1, Figs. l-o. 
Char. gen. Deiititioti a.s in Cladodus. Pectoral tin .supported on liasal .seg- 
ments, of which the anterior articulate with the scapulocoracoid element, and the 
po.sterior to the metapterygium, the whole rorming a nniserisil tin. .Metaptery- 
giuni unsegniented and fused with the basal elements which it .snp|)ort.s. 
The specimen on which this genus is founded throws much light on the struc- 
ture of the Cladodont pectoral tin, and through it, on the question ol'thc evolution 
of this organ among fishes. The fin basis de.scrihed is mostly well pre.scrvcd. and is 
clear as to details of structure. It confirms the characters ascribed by Trat|uair to 
the pectoral fin oi Cladodas from the lower carboniferous of Scotland,' the only 
important difference being that in the latter the metapterygium is distinctly seg- 
mented, while in Sytnmorinm this element I’orins a single piece, except po.ssibly at 
the extremity. According to Tracpiair there is an "oblong” proximal segnnmt of 
the metapterygium, “whose anterior portion seems to have absorbed the basis of 
one or two adjacent rad ials.” \\\ Symmorium reniformc. - aW the l)asals (ratlials of 
Traquair), are fused at their basis with the metai)terygimn. I'lie basals are also 
more numerous than in Dr. Traquair’s shark, for he says “some small radials are 
seen attached to the preaxial side of the first two segment.s — none on the others." 
My specimen agrees with Traquair’s in the absence of basals (radials) from the 
postaxial side of the metapterygium, where indeed they are not to be looked for. 
As this species is the only (JIadodont from the coal measures in which the lin- 
structure is known, it is premature to suppose that all the .s])ecies ol'that liori/on. 
of which there are described, according to Newberry. oS species of the 
genus alone, belong to the gyixwe, Synuiwriuni. But it is not uidikelN- 
that such will prove to b(‘ the ca.se. The name Cladodus is applical)le to the species 
of the lower carboniferous, to which it was originally given by Aga.ssi'/,. where the 
metapterygium is segmented. 
On a knowledge of the fin structure of the paleozoic sharks depiaids the s(e 
lution of the question whether the tri- and plnribasal fins of the modern Elasmo- 
branchs and Teleostomi have been derived from a pinnate archiptcrygiuin as sup- 
posed by Gegenbaur, or from a, lateral fold supported by rays, as sup|M)sed by 
‘ Geological Miiguziiie, Feb., 1888, ji. Sll. 
5e JOURN. A. N. 8. PH I LA., VOL. IX. 
