532 Royal Society^^ - 



lensis, Beryx, Dapidhis orhis, and D, grannlosus ; all of which ap- 

 pear to be constructed according to a common type — one singular 

 modification of which is seen in Palceoniscus comptus and P. Beau- 

 monti, and another in Gyrodus and Aspidorhynchus acutirostris. 

 Still more elaborate complications occur in the scales of the Stur- 

 geon' and of Platysomus parvulus, the minute structure of which 

 is described. Then follow detailed accounts of another interesting 

 group of structures found in the genera Megalichthys, Holoptychkts 

 and Diplopterus, in which the osseous tissues and their superficial 

 coverings are exceedingly beautiful and complicated. The next fish 

 examined is Macropoma Mantelli from the chalk. In this the true 

 bony operculum is studded over with dermal teeth, as is also the 

 posterior part of each scale; the portion of the latter, however, 

 which is subjacent to these dermal teeth, is not osseous, but consists 

 of thin laminas, which do not contain lacunae. The hollow viscus 

 found in the interior of the Macropoma, is shown to be a cylinder 

 of true osseous tissue, of a singular laminated structure full of lacunas. 

 The author rejects the idea of its having been a stomach, but thinks 

 that it may have served the purpose of an air-bladder. 



The structure and arrangement of the dermal teeth from the skin 

 of the Dog-fish are then investigated, and appear to resemble those 

 on the opercular bones and scales of Macrojjoma. Similar teeth are 

 described in the fossil skin of Hyhodus reticulatus, from the lias of 

 Lyme Regis. In the latter, numerous small granules of calcareous 

 matter, having a concentric laminated structure, have been im- 

 bedded in the substance of the soft cutis, under the dermal teeth. 

 The corresponding dermal teeth from the Raia clavata are described, 

 and also those covering the snout of tlie common Saw-fish ; as well 

 as the very singular premaxillary bones of the Ccelorhynchus. 



From an examination of the dermal appendages of the fishes thus 

 cursorily enumerated, the author concludes — 



That what has hitherto been termed enamel, is in fishes a cottii-'' 

 pound structure, separable into ganoin and kosmine (Kocr/ieiv, to 

 adorii) ; the former being transparent and laminated, but otherwise 

 structureless, whilst the latter consists of minute branching tubes re- 

 sembling the dentine of true teeth. 



That the kosmine covering the osseous scales of so many ganoid 

 fish, as in Lepidotus semiserratus, Megalichthys Hibherti, &c., is 

 homologous and identical with the substance composing the dermal, 

 teeth of the true placoids, such as the Dog-fish, Thornback, &c., 

 only that, whilst in the former the areolae of kosmine are aggregated 

 upon bony scales, in the latter they are implanted in the soft integu- 

 ment, witliout the intervention of any bony matter. It follows from 

 this, that the distinction of " ganoid " and " placoid " is scarcely a 

 physiological one, inasmuch as the scales of many so-called ganoid 

 fish, such as Dapidius orbis, Acipenser, &c., exhibit little or no trace 

 of either ganoin or kosmine; that in many of the Placoids these sub- 

 stances are very largely developed ; and that a series of well-defined 

 links exist, passing through the common Thornback, the common 

 Spotted Dog-fish, Hyhodus reticulatus, Macropoma Mantelli^ Da- 



