KI.ASMOIiUANCIlS. 



10G3 



PISCES ELASMOBRANCHII. 



Fishes with cartilaginous endoskeleton (without dermoskeleton), with the shoulder-girdle 

 detached from and suspended behind the head, with the maxillary (and mandibular) bones 

 represented merely by loose cartilages at the sides of the palate and lower jaw, with the 

 branchial arches entirely or partly united to the skin (gill-slits externally open or covered 

 by a common dermal fold), and with diphy cereal or heterocercal caudal fin. Fin-rays 

 primary. Nostrils as a rule ventral. Air-bladder none. 



These fishes were removed from Ahtedi's Chon- 

 dropferi/ffii'' by Boxapakte into a se])arate order, most 

 clear]}- distinguished by the structure of the gills lioth 

 from the ])receding orders, which have borne the com- 

 mon name of Tectohranchii" , as having the branchial 

 cavity co\ered b)- a true opercular apparatus, belonging 

 to the skeleton, and fi'om the lower fishes, the (Jyclo- 

 stomi and J.rptdcdrdii. which are without true branchial 

 arches. The union between these arches and the skin 

 is accomplished in the Elasmobranchs by the extension 

 of n membrane, supported by cartilaginous rods, l)e- 

 tween the latter and each of the former. With this 

 membrane too the several branchial lanaelhv coalesce 

 throughout theii- length. In some Elasmobranchs, in 

 the subordei' nf the Chimseras, however, the said mem- 

 brane extends oiih' in |)art, above and lielow, (piite to 

 the skin, a cdununii branchial cavitv lieing thus pro- 

 duced on cMch side of the bod\'. This cavit%' is fur- 

 nished, as in the preceding fishes, with a single apei-- 

 tm-e, and the rest of it is covered by a dermal flap, 

 extended on cartilaiiinous rods, which are honioloffous 



with the branchiostegal ra3S of the Teleosts, and by a 

 thin disk of cartilage (fig. 294, op), representing the 

 opei'culum of the preceding fishes, but evidently form- 

 ed here, as in the other suborder, by the mutual 

 confluence of the ujjper (posterior) cartilaginous rods 

 at the upper (anterior) end. Analogous cartilaginous 

 rods also appear, as we have mentioned, in the mem- 

 brane originating from each of the branchial arches, 

 and supplying attachments for the branchial lamella^. 

 In the rest of the Elasmobranchs, the suborder of the 

 Sharks and Rays, which is far superior in variety of 

 form, the last-mentioned membrane, sup])orted by its 

 cartilaginous rods (figs. 298 and 300, rhr and hi), is 

 united throughout its extent, both from the hyoid and 

 the branchial arches, either obliquely or in a straight 

 outward direction, to the skin, which opens at the in- 

 terstices into external gill-slits, numbering 7 — .') in the 

 surviving forms of this suborder. 



The scapular and jjelvic arches are far more de- 

 veloped in the Elasmobranchs than in the preceding 

 fishes; and starting from the l^asmobranchs, mor])h(i- 



° An exception is iiinde by ancient (primitive) forms, sucli .'is Cliluniydosclnclic anyuineiw. !\ Jajxinese tisli remarkable in many otlier 

 respects on account of its primitive characters, and described liy ({ai<m.\n. liidl. Mus. Comp. Zool. Hnrv. Coll., vol. XII, No. 1, and Gt'NTHER, 

 Deep Sea Fish., ('hall. Exped., p. 2, pi. LXIV. LXV. 



" See above, p. 1043. 



' Hasse, Jieitr. allgem. iitammesgesdi. UlrMlh., .Jena 1S83, )). 12. 



ScaiHlinavian Fisht. 



134 



