1016 General Notes. 
supports of the external folds, to the proportions and positions — 
which we behold them to present in the different groups of fishes. _ 
IV. The orders of fishes are defined by modifications of the skele- 
ton of lesser significance than those included in statements II. and 
Under this head come modifications in the structure of the 
skull, vertebræ, and fins in which the multifarious character of 
fish evolution has displayed itself, and in which relation to the — 
other classes of Vertebrata does not enter as an element of esti- 
mation. a 
In accordance with proposition III. I define what appear to me — 
to be the primary divisions of the Teleostomi. Before doing sol 
will state the elements of the definition. The supports of all the 
fins consist primitively (in the case of the pectoral fins, the evidence 
‘is only partly in our possession) of at least three longitudinally i 
connected osseous elements. These correspond to what have 
been named (1) the neural and hæmal spines of the vertebræ, (2) 
the axial segments* (interneural and interhæmal bones), and (3) 
the basilar segments? (so called because when present they arè 
; PVA, 
EXPLANATION.—D, DF, dorsal fin; PVF, pectoral and ventral fins; : 
pectoral, ventral, and anal fins; AZ, anal hg NSP, neural spine; Dap, tite j 
pophysis; AS, hæmal spine; Axo, axonost; Bo, baseost. 
* Proc. Amer. Philos. Society, 1877, May. org’ 
? Cope, Transactions Prend Phils: a EA 1870, p. 4453 Ryder, “ot US 
of Heterocercy and the Evolution of the Fins and Fin-Rays of gr and “ 
Fish Cémmission, 1886, pp. 985, 1017. The terms “ actinost” (Gil ) 
phore” (Ryder) were subsequently applied to the basilars. 
