PHYLLODUS. 139 



fish to which they have belonged, present a contour somewhat like 

 that of a simple leaf: the posterior part being contracted, as if 

 for the attachment of a stalk, the opposite end being rounded and 

 thinned off. The largest specimen of this fossil, which I have 

 yet seen, is figured in Plate 47, fig. 1 and 2. It consists of an 

 anchylosed mass of superimposed more or less flattened, lamel- 

 liform teeth, of which those forming the middle longitudinal row are 

 the largest, and present a transversely elongated oblong figure : these 

 are surrounded by smaller oblong dental lamellae, irregularly placed, 

 and diminishing in size to the circumference of the mass, where they 

 exchange the oblong for a circular form. All the dental lamellae are con- 

 vex on the upper surface (fig. 1) and concave on the under surface (fig. 2.) 

 On a superficial inspection the middle lamellae might be supposed to be 

 as thick as the mass of which they form part, but this is evidently not 

 the case w^ith the marginal lamellae ; these are seen to be superimposed 

 in nearly vertical tiers, like the lamellae of the maxillary dental mass 

 in theDiodon. The number of lamelliform teeth in each pile, increases 

 from the anterior to the posterior part of the mass, where, in the 

 specimen figured, nine or ten denticles might be counted in a single 

 tier. To ascertain whether the large middle teeth were also lamelli- 

 form, and similarly superimposed, I had made, by the kind permission 

 of Mr. Bowerbank, a vertical section through a dental mass of the 

 same species of Phyllodus as the one figured, and found that the same 

 lamellar condition and arrangement pervaded all the teeth. Between 

 the upper and the lower of the two longest median denticles, there 

 were interposed six plates similar to the two superficial ones of which 

 the upper surface is shown in figure 1 , and the lower surface at 

 fig. 2. A magnified view of a thin transparent slice taken from the 

 surface of the vertical section, including a portion of four of the super- 

 imposed plates of two contiguous piles, is given at Plate 44, figure 2. 

 It displays a structure analogous in essential points to that of the 

 pharyngeal teeth of the Scarus. If, for example, the cone, of which 

 a section is figured at Plate 52, were flattened down and rolled out, 

 it would form a lamelliform tooth composed of a layer of enamel and 

 a layer of dentine of equal thickness, supported on a thinner layer of 

 coarse cellular bone. Such is the microscopic texture of a single 



