24 SHOULDER-GIRDLE AND BREAST-BONE. 



uro-hyal all these are subcutaneous, and the skin over them is very thick. The endo-skeletal 

 skull-elements, like those of the rest of the skeleton, are converted into strong fibrous bone, and 

 it is impossible that any of them should be seen from without, seeing they are all covered with 

 the dense ganoid helmet. This splendid armour must be removed before the prae- and post- 

 frontals, the ethmoids, the pterotics, the epiotics, and the supra-occipital can be displayed on the 

 upper part of the head ; the Shoulder-girdle, also, is almost entirely hidden within the huge 

 enamelled shoulder-plates; the gleuoid bosses just peeping out between the joints of the harness 

 (see fig. 9, gl.). 



On the head there may be seen the quasi-ethmoid or meso-nasal (Plate I, fig. 9, m. n.) ; 

 two nasals (n.) ; two frontals (f.), separated by a large fontanelle (fo.) for the most part, but 

 united by suture at each end ; two lachrymals or prae-orbitals (1.) ; two suborbitals (su. o.) ; two 

 post-orbitals (pt. o.) ; two dermo-post-frontals (d. pt. f.) ; one large parietal (p.) ; two large 

 dermo-supra-occipitals (d. s. o.) ; two dermo-epiotics (d. ep) ; two large supra-temporals (s. t.) ; 

 and two operculars (op.). Each frontal is pierced near its middle, and each dermo-post-fronta[ 

 near its lower margin, for a mucous duct. Each supra-temporal is pierced in four places for 

 ducts, and slit through near the top to form the spiracular chink. Behind these plates the whole 

 body is enveloped in a right and left series of supero -lateral plates, and the same of infero-lateral 

 plates ; the first cincture is further subdivided over the Shoulder-girdle, and the last cincture over 

 the base of the tail-fin. The supero-lateral bones are directed downwards and forwards, the 

 infero-lateral downwards and backwards (Plate I, fig. 9) ; they end in a blunted triangle, and 

 the lower part of the upper plates overlaps the upper part of the lower. The upper and lower 

 plates are very much alike ; they are equally arcuate, equally convex (at their junction they form a 

 shallow furrow), and of equal width and length ; but there is this difference, namely that near their 

 base the upper ones are pierced in front and notched behind for mucous glands. If this portion 

 were cut off by a suture in each upper plate we should have the " lateral-line" mucous bones of 

 typical Teleostei ; this does take place in the first cincture (fig. 9, p. t.) ; this tuberous, doubly 

 notched bone being the supra-scapula of authors, but entitled "post-temporal" in this Memoir. 

 There are twenty-five of these cinctures, which are not perfect either above or below, as they 

 leave a space both on the spinal and the abdominal line. Above, the broad-topped supero-laterals 

 of the first body-belt meet by a long suture, like the symmetrical dermo-supra-occipitals (d. so. 

 s. 1. 1) ; the second supero-lateral, which has undergone no segmentation below, scarcely meets its 

 fellow of the opposite side, but, retiring from it behind, leaves an interspace which is filled up 

 by a highly polished, crescentic, dermo-spinal (fig. 9, d. sp. 1). Next behind this comes the 

 symmetrical, but coalesced, first ray of the first dorsal fin (d. sp. 2) ; it is a stout, sharp spine. 

 Then follow seven feebler, symmetrical, jointed rays, and these are succeeded by ten polygonal 

 ganoid plates (fig. 10, d. sp., shows five of these), which begin to be ridged and spinous behind, 

 the last but two having a small prickle, and the last a strong spine ; these have the single 

 coalesced spine of the "second dorsal" coming next; then the dermo-spinals are absent over two 

 cinctures, where the little fin-flap is attached: behind the "second dorsal" there are three or 

 four symmetrical bones, flat at first, but passing gradually into the strongly spinous, symmetrical 

 rays that form the base of the upper lobe of the " caudal fin." 



Below, the small subcutaneous " basi-branchiostegal/' the so-called " uro-hyal " is the only 

 azygous bone until we come to the space between the " anal fin " and the lower lobe of the 

 " caudal fin ; " in that interspace there are two very convex ganoid plates, followed by the sym- 



