296 '/ K. Thacher — Median and Paired Fins. 



the stem-row {Stamm-relhe) , a long taperiug many-jointed cartilaginous 

 rod which bears on the outer side a series of rays. Tliis evidently 

 calls for no change of view regarding the Enaliosaurs or Stapedifera. 

 But the fin-skeleton of iishes exhibits everywhere, except in Pro- 

 topterus and Sct/mnus, a slipping off of the rays from the stem-row" 

 and their articulation with the girdle, and very commonly their artic- 

 ulation with one another and considerable fusion (concrescence). 



Still another change awaits the primordial limb, even the named 

 archipterygium. In 1871, Gtinther* published his description of 

 Ceratodus. Here the stem-row has a series of rays down each side. 

 The archipterygium is modified to accord with this in the Jena 

 Zeitschrift published x\pril 22, 1872,f where Gegenbaur adopts the 

 " Biseriale Archipterygium'''' as the parent form, and attempts to 

 show that there are some traces of the median row of rays in the 

 pectoral fins of some Elasmobranchs. With the exception of Cerato- 

 dus and the questionable exception of these Elasmobranch pectorals, 

 the biserial has been everywhere reduced to the uniserial form, and 

 still further reduced as heretofore explained. 



In the third volume of the Untersuchungen, dated May, 1872, a 

 suggestion J: is made of the possible origin of the Archipterygium and 

 the limb-girdles. They are assimilated to tlie branchial arches and 

 their diverging rays, where rays move up upon, and articulate with, 

 the longest middle ray. It is but justice to say that the suggestion is 

 a little vaguely and liesitatingly made. 



In confirmation of Gcgenbaur's views, Bunge,§ in 1874, published a 

 further investigation of the pectoral fin of Elasmobranchs, showing a 

 number of rays which might be regarded as median, in several species 

 not examined by Gegenbaur. Finally, in 1876, Huxley || took up the 

 question, and, wliile he accepted the archipterygium, he modified the 

 interpretation of a large number of the forms. 



*Proc. Roy. Soc, 1871, p. 378, and more fully, with a figure of the fin-skeleton, in 

 Ann. and Mag. of Nat. Hist., March, 1871. To these Gegenbaur refers, Jen. Zeitsclir., 

 Bd. vii, Hft. 2, p. 132, note. But a much fuller description is given by Giinther, Phil. 

 Trans., vol. clxi, pt. ii, pp. 511-572. This vs^as pubhshed early in 1872. 



f Jen. Zeitschr.. Bd. vii, Hft. 2, pp. 131-141. Gegenbaur, Ueber das Archip- 

 terygium. 



:}; Gegenbaur, Unters., Hft. III. Kopfskelet der Selachier, p. 181, note. 1872. 



§ A. Bunge, Jena. Zeitschr., Bd. 8, Hft. 2, 1874. Ueber die Nachweisbarkeit eines 

 biserialem Archipterygium bei Selachiern und Dipnoern. Bunge also calls attention 

 to the fact that the fringing rays in Protoptems a-i,nectens are on the median (i. e., ven- 

 tral,) side of the axis, and not, as in Elasmobranchs, on the lateral (i. e., dorsal,) side. 



II T. H. Huxley, Proc. Zool. Soc. Lon. for 1876, PI. 1. On Ceratodus Forsteri. 



