THE SHOULDER-GIRDLE IN FISHES. 25 



metrical rays of the lower caudal lobe. There is no true spinal derm-bone in the head ; the first 

 body-belt has none (s. 1. 1) ; the two supra-occipital derm-bones, the single parietal, the sym- 

 metrical frontals, the single dermo-ethmoid, 1 all these are serial homologues, whether azygous or 

 symmetrical, of the upper three fourths of the supero-lateral plates, and not of the dermo-spinals 

 (Plate I, fig. 10, d. sp.). The segment which is cut off from the first " supero-lateral," and 

 which is continuous in all the rest, save the last, or 25th, reappears (homologically) in the 

 head, as the supra-temporal (s. t.) ; then this series becomes double, and we have the " dermal 

 post-frontal" (d. pt. f.), post-orbital (pt. o.), sub-orbital (su. o.), lacrymal (1.), and nasal (n.). 

 The first infero-lateral plate is subdivided on the left side into two, and on the right side into 

 three plates ; these are in relation with the Shoulder-girdle, and may be called supra-clavicle (s. cl.), 

 clavicle (cl.), and inter-clavicle (i.cl.) : I shall describe these anon. But this subdivision becomes 

 greater in the head ; the opercular (op.) repeats the supra-clavicle, and the sub-opercular (not 

 present in this Fish) the clavicle : in this, the " hyoid " dermal cincture, we have, below, the 

 branchiostegals, and the so-called uro-hyal as a lower spine-bone. In this Fish, as in the Cypri- 

 noids, there are only three branchiostegals ; but in " the clupeoid Elops there are more than 

 thirty" (Owen, 'Lectures,' vol. ii, p. 115). This lower part is thus seen to correspond with the 

 inter-clavicular region. The opercular has the squamosal (pre-opercular) as its homotype, and the 

 sub-opercular is preceded by the inter-opercular (see Huxley and Hawkins's ' Atlas,' plate 5, fig. 2, 

 where the letters P. op. are by mistake put to the quadratum of Lepidosteus ; the pre-opercular is 

 the large sickle-shaped bone above I. op.). The lower hyoid and the inter-clavicular regions have 

 their homotypic scales in the jugulars (not present in Callichthys) and in the splints of the man- 

 dible : the splints (subcutaneous bones) in front of and above the mouth must be left until I have 

 time to work out the whole skull ; the premaxillaries, maxillaries, jugals, quadrato-jugals, pterygo- 

 palatine splints, and parasphenoid, all come under this category, and must all be studied in 

 relation to the bony armour generally. Nevertheless, what has just been written is necessary for 

 right views upon the parts that enclose, and often become isomorphic of, the true Shoulder-girdle. 

 I must now return to these Shoulder-plates, but the post-temporal need not be further described. 

 The supra-clavicle (fig. 9, s. cl.) is an oblong plate, turned obliquely downwards and forwards, 

 and overlapping the equally oblique upper margin of the clavicle (cl.) ; it is not separate from the 

 clavicle on the left side, but the subcutaneous peg which articulates with the post-temporal is 

 seen in figs. 11 and 12, notwithstanding its connate condition in that left plate. It has a large 

 ganoid surface ; the subcutaneous part being the process which passes within the post-temporal ; 

 the antero-superior margin, which is overlain by the supra-temporal; and the antero-inferior 

 margin, which passes within the operculum (fig. 9, s. cl., p. t., s. t., op.). ' 



The clavicle (figs. 9, 11, 12, and 13, cl.) of Callichthys would not, at first sight, be recognised 

 as such ; this arises from the continuity of its essential part with a large ganoid plate : this plate is 

 distinct in the Lophobranchii ; and thus the typical clavicle is at once understood. The outer 

 aspect of this bone (fig. 9) is that of a triangle, with the anterior angle produced downwards and 

 inwards, in front of the inter-clavicle (i. cl.) : but there is a large subcutaneous plate hidden in 

 this aspect, which forms the hinder wall of the gill-opening. The concave anterior aspect of this 



1 This bone is enough to deceive the shrewdest anatomist ; it is truly a meso-nasal : Professor 

 Owen's " nasal " (see ' Lect.,' vol. ii, p. 100) is the true " ethmoid," and lies beneath it : it is lettered 

 eth. all through Mr. Huxley's Memoir. 

 4 



