356 MEMOIRS OF THE CARNEGIE MUSEUM. 



hand, they agree with these famiUcs and differ from almost all other fishes, in the 

 same respects as those in which the families just mentioned have been shown to 

 agree with one another; viz., the number of the dorsal fins, the location of the paired 

 fins, the absence of branchiostegal rays and their replacement by jugular bones." '^ 



In a subsequent memoir the author whom we have just quoted speaks as 

 follows regaring the extraordinary conservatism and persistence manifested by 

 the group of Coelacanth fishes ever since its introduction :'' 



" Bearing in mind the range of the Coelacanths from the Carboniferous [since 

 ascertained to extend from the Devonian] to the Chalk formations inclusive, the 

 uniformity of organization of the group appears to be something wonderful. I have 

 no evidence as to the structure of the base and side-walls of the skull in Coelacanthus, 

 but the data collected in the present Decade shows that, in every other particular, 

 save the ornamentation of the fin-rays and scales, the organization of the Coelacanths 

 has remained stationary from their first recorded appearance to their exit. They 

 are remarkable examples of what I have elsewhere termed ' persistent types,' and, 

 like the Labyrinthodonts, assist in bridging over the gap between the Paleozoic 

 and the Mesozoic faunse." 



The chief feature in which this family shows specialization is in the large sym- 

 metrical caudal fin, which exhibits a series of supports directly apposed to the 

 neural and haemal arches, equalling in number both these and the overlapping 

 dermal rays. It is also specialized, as noted by Dr. A. S. Woodward,^ in the 

 following respects: (i) the fusion of the bones of the pterygoquadrate arcade; (ii) the 

 reduction of the inf radentaries to one ; (iii) the reduction of the opercular apparatus 

 to one operculum on each side and a pair of gular plates ; (iv) the loss of the baseosts 

 in the anterior dorsal fin ; and (v) the ossification of the air-bladder. 



Genus Undina Miinster. 

 "Teeth absent on the margin of the jaws, but a few hollow, conical teeth within. 

 Supplementary caudal fin prominent; the rays of all the fins broad and robust, 

 often expanded, and closely articulated in the distal portion; small, upwardly- 

 pointing denticles on the preaxial rays of the first dorsal and caudal fins. External 



' Huxley, T. H., Preliminary essay upon the systematic arrangement of the Fishes of the Devonian 

 Epoch, prefixed to the tenth decade of Figures and Descriptions illustrating British Organic Remains 

 (1861, p. 20). 



' Huxley, T. H., Illustrations of the Structure of the Crossopterygian Ganoids. Memoirs of the 

 Geological Survey of the United Kingdom, Decade XII., 1866, and reprinted in the supplementary volume 

 of the Scientific Memoirs of Thomas Henry Huxley, 1903, p. 65. 



8 Outlines of Vertebrate Palaeontology, 1895, p. 78. 



