378 I^^^of. Kncr on Xenacanthus Dechenii, 



girdle is similar to that in the sharks ; the scapular arch is not 

 attached to the occiput, but lies further back, as in CJwndropteri and 

 eels, without any immediate connexion with the vertebrae, — the 

 neurapoi^hyses of eight vertebrae lying between it and the head. 

 There is no vestige of an opercular apparatus. The scapular arch 

 is formed of at least three separate portions, — supra-scapula, scapula, 

 and clavicula. The inferior triangular pharyngeal bone is single, 

 and like the two superior separate ones they are closely covered 

 with teeth of the same kind as those of the jaws ; its posterior end 

 lies directly before the scapular arch. From the occiput arises a 

 straight-pointed occipital spine, without any basal articulation, some- 

 what depressed at the base, rounded towards the point, and serrated 

 on both its lateral margins. The simple-rayed dorsal fin begins 

 before the point of this spine (which is always laid down in a back- 

 ward direction), and not only runs along the whole back to the 

 point of the long compressed, and rather attenuated tail, but is also 

 continued on the ventral side of the body towards the few-rayed 

 anal fin. The pectorals are inserted at the angles of the scapular 

 arch, and begin with some rather long, broad, bony plates, and a 

 long multi-articulate carpal bone, to which were affixed several 

 oblique, thin, long rays, continued by filamentous fibres, thus re- 

 calling the pectorals of the sharks but not specially those of Squatina. 

 The anal fin is also distinguished by a strong dichotomous carpal ray. 

 The ventral fins are always situated at, or behind, the centre of the 

 body, and supported by triangular pelvic bones. In some specimens 

 they are coalesced into a ventral disc, and provided inside and behind 

 with tubiform (or half-tubiform) clasping appendages, others are 

 without these, and are separate from each other. The vertebral 

 column runs in a straight line to its extremity, and is composed of 

 numerous vertebral elements, superior and inferior arches with 

 spinous processes, and bearing thin ribs on the anterior arches ; the 

 dorsal fin is supported by a double (superior and inferior) row of 

 hollow interspinous and dichotomous accessory interspinal bones 

 (syropophyses, Ag. ) articulating with each other, and with the fin- 

 ra3^s by true articulations. The vertebral bodies were nowhere truly 

 developed, and failed in the caudal region altogether. The skeleton 

 was probably mostly cartilaginous, as demonstrated by the distinct 

 impression of the outer mosaic-shaped (tessellated) bony crust, quite 

 similar to that of the living Chondropteri. The dermal covering in 

 other examples consisted of a granular shagreen, composed of very 

 small enamelled scales." 



For several reasons (especially the difference of the teeth, which 

 are smooth in some, furrowed in others, the different length, shape, 

 and armature of the occipital spine, the dermal covering, etc.), the 

 author is inclined to assume the existence of more than one species 

 under the collective name of X. Dechejii, (the species from Lebach 

 might perhaps be distinct from that of Rakowitz). 



The difference in the structure of the ventral fins, Professor Kner 

 most ingeniously interprets (and herein I heartily agree with him), 

 as a sexual difference, the ventral disc with its clasping appendages 



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