THE SHOULDER-GIRDLE IN FISHES. 29 



brachials (fig. 2 C, b.) ; they are flat, but thick, and the upper is twice as large as the lower ; 

 they are articulated to a ridge of the inter-clavicle ; for the large complex condyloid facets of 

 the great, serrated dermal spine of the pectoral fin takes up the room due to these true 

 limb-rays, and acquires, moreover, a large amount of articular surface on the clavicle and inter- 

 clavicle besides. The remarkable trumpet-shaped cavities behind and below S. S. and S. 0., shown 

 in Professor Huxley's figure ('Mem. on Gan.,' p. 30, fig. 20), belong to the "atlas" and "axis" 

 vertebrae, and they are strongly attached to the post-temporals and clavicles at their point of 

 junction ; they lodge the lateral cornua of the three-lobed air-bladder. These cavities are very 

 imperfect below ; but this deficiency is largely supplemented by a transverse splint on each side, 

 attached, below, to the anterior edge of the great semi-cylinder of the "atlas." There is a 

 smaller splint in each cavity, and two still smaller splints eke out the mouth of each of these 

 trumpets. The large obliquely transverse splints (they are somewhat turned backwards) meet 

 within a line and a half below the centrum of the " atlas ;" between and behind the splints, this 

 and the next centrum are deeply grooved. 



I mention this structure to exclude the attached splints from the clavicular category, although 

 I shall have to describe a splint similar to the largest which is really correlated to that system in 

 Ostracion ; also to show the relation of this structure to what is seen on one hand in the Cypri- 

 noids, and on the other in certain Gadoids, e.g. in the Hake (Merlucius vult/aris, Cuv.). 



Nor, in considering the multifarious affinities of this type, must the elegant gill-arch 

 flaps, with their cartilaginous rays, be forgotten ; a structure repeated from the Plagiostomes : 

 nor must we omit to mention the remarkable dendritic gill-tufts in this Fish which made Geoffrey 

 give it the title Heterobranchus (Clarias, Gronovius). (See Cuvier's ' Animal Kingdom/ Griffith 

 and Hamilton Smith's Transl., p. 408.) 



The figure given by Professor Huxley (op. cit., p. 34, fig. 20, from Cuv. and Valenc. 

 ' Hist. Nat. des Poiss.') of Arius rita shows the heart-shaped ganoid portion of the " post- 

 temporal," and directly below it an enormous oblong plate, which is the outer part of the 

 clavicle. It is possible that if this were examined carefully, an inter-clavicular portion might be 

 seen even from the surface. On the next page (fig. 21) there is an outline sketch of the hyoid 

 and thoracic plates of Zoricaria, seen from below. In this figure, c is the clavicle ; d the 

 inter-clavicle. In the Hunterian Museum (see ' Osteol. Catal./ vol. i, p. 23, No. 70) there is a 

 very valuable skeleton of a Silurus, in which the inter-clavicles are very strong ; and where the 

 post-temporals and clavicles have a ganoid portion, the former is bifurcate above, thus showing 

 an approach to the ordinary Teleostei. 



FOSSIL SILUROIDS. 



In the Memoir just quoted, Professor Huxley (pp. 29 37) gives his reasons for placing 

 Coccosteus "in a place near, if not among, the Siluroideij" fig. 19, p. 30, shows an outline plan 

 of the skull of this extinct Fish. Here 8, s, is the post-temporal plate ; and d, the next supero-lateral 

 plate its serial homologue. The clavicle is lettered c, and it seems to have no supra-clavicular 

 bone segmented from it. The large bones below are best seen in fig. 21, p. 35 ; where c is the 

 huge inter-clavicle ; and it will be seen that in this bone we have the counterpart of the lowest 

 bone in the dermal Shoulder-girdle of the Sturgeon (Plate I, figs. 68). In the Siluroids the 



