THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE IV. VOL. II. 



No. IX.— SEPTEMBEE, 1895. 



OE-ia-izsTJLXj .A.I^TI0Xi:BS. 



I. — On the Structure of the Frontal Spine and the Kostro- 



LABiAL Cartilages of Squaloraja and Chimera, 



By Otto M. Eeis, Ph.D. ; 



Assistant in the Oberhergamt, Munich. 



(PLATE XII.) 



THE remarkable frontal spine of Squaloraja has always been 

 described as a dermal structure by those who have referred to 

 it, and has been classed with the shagreen-granules and dentition. 

 After the systematic position of the genus had been determined,^ its 

 frontal spine was rightly recognized as identical with the spine-like 

 frontal process in ChinKera and fossil Holocephala, with which it 

 was formerly compared by W. Davies ^ and A. S. Woodward.^ Both 

 these processes were regarded as dermal structures by von Zittel,* 

 Jaekel,* and A. S. Woodward,^ and treated as true ichthyodorulites, 

 i.e. as if consisting of dentine or vasodentine. In 1890 the present 

 ■writer briefly pointed ouf that the frontal spine of the Jurassic 

 Chimseroid, Ischyodiis avita, consisted of extremely calcified fibro- 

 cartilage, resembling that of the so-called "claspers" of all male 

 Elasmobranchs. The microscopical structure of these parts differs 

 conspicuously from that of the calcified granules in the common 

 (hyaline) cartilage of the internal skeleton, and its ontogenetic 

 development is different. 



It is necessary to describe these differences in detail, because 

 0. Jaekel ^ refers to the frontal spine as having the same structure 

 as the rostral prolongation. With regard to the rostrum he says — 

 " It consists of a hollow calcified tube, the peripheral parts of which 

 consist of little fused cones on which separate star-shaped dentine- 

 scales are fixed." ^ The following pages will show that this statement 

 cannot be based upon accurate observations. They relate to two 



^ A. S. Woodward, Cat. Foss. Fishes Brit. Mus., pt. ii, p. 40 (1891). 



2 W. Davies, Geol. Mag., Vol. IX, p. 145, pi. iv (1872), 



3 A. S. Woodward, Proc. Zool. See. 1886, p. 527. 



* K. A. von Zittel, Handb. Palseont., vol. iii, p. 95. 



^ 0. Jaekel, Sitzungsb. Gesell. naturf. Freimde, BerHn, 1890, pp. 120, 127, 



" A. S. Woodward, op. cit. 1891, p. 40. 



7 0. Eeis, Geognostische Jahreshefte, 1890, p. 8. 



8 0. Jaekel, Die Selachier vom Monte Bolca (Berlin, 1894). 



9 "Es besteht aus einer hohlen Kalkrohre deren peripherische Teile aus zusam- 

 mengeschmolzeuen Kiigelchen bestehen, worauf vereinzelt sternformige Dentin- 

 Bchuppen sitzen" {op. cit., p. 65). 



DECADE IV. VOL. II. — NO. IX. 25 



