80 SIXTEENTH REPOUT ON THE CABINET OF NAT. HISTORY. 



Fig. 2, is a distorted portion of the last volution, preserving a well-defined outline. 



SPIROPHYTON TYPUM. 



PLATE II. FIGS. 1, 2, 3. 



Frond spiral, slowly ascending, with six or more volutions, some- 

 , what rapidly expanding at each turn of the spire. Frond thin : 



surfaces striated or finely wrinkled, sometimes grooved parallel 



to and near the outer margin, with the perijDliery thickened. 



Spaces between the volutions three or four times greater than the 



thickness of the frond. 

 Surfaces of the discs deeply and abruptly concave near the centre, 



and slightly concave or sometimes nearly flat on the outer half : 



margins clearly defined. 



Fig. 1. Upper side of the frond, at about the sixth or seventh volution from the base. The dark 

 line of shadow from the centre to the lower side indicates the thickness of stone 

 intercalated between two of the A'^olutions. 



Fig. 2. A transverse section of the same individual, about two volutions lower; looking upon 

 the lower side. There is a shallow groove and slight thickening of the periphery. 



Fig. 3. A partial restoration of a frond of this species, derived from the examination of spe- 

 cimens similar to figs. 1 & 2. 



SPIROPHYTON VELUM. 



Fucoides velum ; Vanuxem, Geological Report, p. 176; figs. 391 & 160. 



This species appears as irregular expansions like the one figured 

 by Mr. Vanuxem. The surface is marked by undulating ridges, 

 which become stronger on the sides, and are not entirely parallel 

 with each other or with the outer margin ; each one having been at 

 one time the exterior limit of the frond, which clianges the curva- 

 ture of its outline in its fidvancing growth. 



