388 Br. Otto M. Reis — Structure of Sqiialoraja and Chimo&ra. 



as proving that the spine consists primitively of paired elements, 

 a conclusion also suggested by the bilatei'ally symmetrical disposition 

 of the blood-vessels in the wall of the spine of the adult male Chimcera 

 a,nd Squaloraja. 



This result is interesting in view of the present writer's former 

 expression of belief that the three pairs of parietal spines of Menaspis 

 (Fig. 9, phi, phji, phjn) are the paired serial homologues of the azygous 

 frontal spine of the male Holocephala. JaekeP has referred these 

 horn-like spines to the vasodentine skeleton, at the same time 

 including the frontal spine of Holocephala among vasodentine 

 ichthyodorulites. 



The disposition of the dermal vasodentine plates in Menaspis as 

 compared with the parietal horns, agrees with that of the paired 

 plates of the Myriacanthidee (e.g. Chimcsropsis, Fig. 3) as compared 

 with their frontal spine. A Myriacanthid spine with overlying 

 tubercles is shown in Fig. 11, and may be compared with Fig. 9, 

 which exhibits the left half of the cranium and trunk in Menaspis, 

 with the three parietal (male) horns, the lateral spine, and the flat 

 conical plates behind. Jaekel may have been led to identify vaso- 

 dentine in the parietal horns of 31enaspis (if he has had occasion 

 to study satisfactory microscopical sections of splints of them) by 

 the abundant occm-rence of canals for blood-vessels, which are also 

 observable in the male frontal spine of Chimaira, Ischyodvs, and 

 Squaloraja. 



We come now to the consideration and restoration of the rostro- 

 labial appendages of Squaloraja. Before having established the 

 systematic position of the genus, A. S. Woodward described its great 

 rostral prolongation as an " intertrabecular cartilage." Now we 

 must regard it as identical with the corresponding cartilage in 

 CJiimcera (Fig. 8), and the lateral cartilages, which A. S. Woodward 

 terms "prepalatine," will also be seen to be the same as in the 

 last-mentioned genus. The rostrum of the Selachian BMnohatus 

 maronita, however, is nearly identical with that of Squaloraja.^ 



Finally, there are the labial cartilages of Squaloraja, of which 

 A. S. Woodward recognizes two pairs (Fig. 6, a, h), comparing 

 them with the rods which form the axes of the oral barbels in the 

 Myxinoids. According to the new view, it is now necessary to 

 compare them with the labials of Cliimcera. 



These appendages of ChimcEra are insufficiently described by 

 Hubrecht,^ and it is therefore necessary to treat of them more in 

 detail. Three segments of cartilages may be distinguished in the 

 labial complex. The first segment (I) is a single cartilage ("nasal 

 wing cartilage" of Hubrecht), fixed in the common rostro-labial 

 connective tissue, which also supports the great median cartilage of 

 the second segment. The latter consists of three cartilages, of which 

 the great median piece Ila is covered throughout its whole length 

 by the labialis anterior muscle,* and thus cannot be a " Schnauzen- 



1 0. Jaekel, Sitzungsb. Gesell. naturf. Freunde, Berlin, 1890, pp. 119-131. 



2 See Catal. Foss. Fishes Brit. Mus., pt. i, pi. iii, fig. 4. 



3 A. A. W. Hubrecht, Niederland. Archiv., vol. iii, pp. 255-272 (1876). 



4 B. Vetter, Jena Zeitschr. f. Naturw., yoI. xii, p. 443 (1878). 



