434 RAMBLES OP A GEOLOGIST. 



isms, chiefly ichthyolites. I saw among them several good 

 specimens of the genus Pterichthys, and of what is elsewhere 

 one of the rarer genera of the Dipterians, the Diplopterus. 

 A well-marked individual of the latter genus had, I found, 

 been misnamed Dipterus by some geological visitor who had 

 recently come the way, a mistake which, as in both ichthyo- 

 lites the fins are similarly placed, occasionally occurs, but 

 which may be easily avoided, when the specimens are in a 

 tolerable state of preservation, by taking note of a few well- 

 marked characteristics by which the genera are distinguished. 

 In both Dipterus and Diplopterus the bright enamel of the 

 scales was thickly punctulated by microscopic points, the 

 exterior terminations of funnel-shaped openings, that com- 

 municated between the surface and the cells of the middle 

 table of the scale ; but the form of the scales themselves was 

 different, that of the Dipterus being nearly circular, and 

 that of the Diplopterus, save on the dorsal ridge, rhomboidal. 

 Again, the lateral line of the Diplopterus was a raised line, 

 running as a ridge along the scales ; whereas that of the Dip- 

 terus was a depressed one, existing as a furrow. Their heads, 

 too, were covered by an entirely dissimilar arrangement of 

 plates. The rounded snout-plate of the Diplopterus was sud- 

 denly contracted to nearly one-half its breadth by two semi- 

 circular inflections, which formed the orbits of the eyes ; full 

 in the centre, a little above these, a minute lozenge-shaped 

 plate seemed as if inlaid in the larger one, the analogue, ap- 

 parently, of the anterior frontal ; and over all there expanded 

 a broad plate, the superior frontal, half-divided vertically by 

 a line drawn downwards from the nape, which, however, 

 stopt short in the middle ; and fretted transversely by two 

 small but deeply-indented rectangular marks, which, crossing 

 from the central to two lateral plates, assumed the semblance 

 of connecting pins. The snout of the Dipterus was less round ; 

 it bore no mark of the eye-orbits ; and the frontal buckler, 



