Br. Otto M. Reis— Structure of Sqmloraja and CJiimcera. 387 



exhibits the irregular peripheral lamellation which is often observ- 

 able in the lines along which the cells of calcified hyaline cartilage 

 are disposed.^ This microscopical structure is identical with that of 

 theclaspers of fossil and living Plagiostomes and Holooephala,- in 

 which the vascular canals are only seldom wanting. The micro- 

 scopical structure of the middle cone of Selachian vertebraj and of 

 the calcified gill-filaments in the Teleostomous fishes, is also similar. 

 The structure is, indeed, to be defined as fibrous cartilage, or, more 

 technically speaking, as a prochondral diiferentiation of the mesoderm, 

 of which the intercellular substance ("Bindesubstauz ") has not yet 

 undergone the change into the later hyaline stage. 



The fibrous cartilages of the male appendicular skeleton are 

 produced in the corium by scleroblasts of a kind which never form 

 hyaline cartilage in fishes. They are developed in dermal folds, 

 originally unconnected with the endo-skeleton of the pelvic fin, 

 aad only joined secondarily with the latter.^ The frontal spine of 

 Chim^roids is similarly quite separate from the cranium, and 

 essentially a part of the fibrous and vascular layer of the cutis. 



The cells of these calcifications, which we must now term 

 "cutaneous," are not only irregularly elongated, but are also much 

 more numerous than in the cartilages of the endo-skeleton. I have 

 already pointed out ^ that there is a remarkable difi'erence in the 

 number of cells exhibited by fossilized fibrous cartilage and hvaline 

 cartilage ; the cells very frequently disappear entirely in the latter, 

 and are only rarely seen in certain parts of its calcifications. I have 

 observed the same phenomenon in the superficial granules of the 

 endo-skeleton in the living CUmcera, which agrees with the fossil 

 Ischi/odus, Chimceropsis, and even with Squaloraja. The difi'erence 

 may be observed in the fibrous and hyaline cartilage of one and the 

 same specimen. 



The second British Museum specimen under consideration (PI. XII, ■ 

 Fig. 1) exhibits the great median rostral prolongation. Its dorsal 

 and ventral layers of calcareous prismatic granules are slightly dis- 

 placed at the ends. On the surface are scattered several of the little 

 hopked clentine tubercles, lying with their radiated bases upon the 

 prismatic granules of the calcified hyaline cartilage ; and these seem 

 to be in a perfectly natural position. Near the lateral border of the 

 proximal end of the rostrum, there is also a noteworthy lamellar 

 deposit of bone-like substance. The bony aspect and yellowish-grey 

 colour of this are suggestive of the proximal end of the male spine, 

 of which the deposit may perhaps be a few splints. A microscopical 

 section of the substance confirms this idea, and clearly shows calcified 

 cutaneous fibrillar cartilage. The specimen may thus be either (i) 

 the dorsal aspect of the rostrum of a male with rudiments of a spine, 

 or (u) the ventral aspect of such a rostrum showing paired ventral 

 spines, or (iii) the dorsal aspect of the rostrum of a female. The 

 latter supposition seems most probable, and I regard the specimen 

 1 W. C. Williamsou, Phil. Trans. 1851, pi. xxx, fig. 30. 



J. Eiess, Palfeontogr., vol. xxsiv, pi. ii, fig. 12 (clasper of Chimcefa). 

 3 Petri Zeitschr. f. wiss. ZooL, xxs, 1878, p. 325. 

 0. Eeis, Mikroscop. ArcMv., yol. xli, p. 569. 



