110 Hall on the 



through the centre, the cells of the parts laterally compressed, 

 would be seen with the mid-rib not strictly defined ; and the bases 

 of the cells of that part vertically compressed, scarcely or not at 

 all visible. When a small portion of the base of that part which 

 is vertically compressed is preserved, the bases of the cells remain 

 and mark the axis. When instead of being imbedded so that two 

 parallel sides are compressed laterally and the other vertically, the 

 whole frond lies in an oblique position, the two adjacent rectan- 

 gular parts are spread open and flattened upon the surface of the 

 slate, the specimen then appears as if the cells Were conjoined at 

 their bases, or as if separated by a filiform mid-rib. An individual 

 compressed in this manner and then separated through the 

 middle, will present the bases of the two adjacent divisions with 

 the cells lying obliquely to the plane of the slaty laminae. These 

 and other varieties of appearance are due to the position in which 

 the fossil was imbedded, and the direction of the cleavage or lami- 

 nation of the slate. 



Phtllogeaptus. (New Genus.) 



Description. — Frond consisting of simple foliate expansions, 

 celluliferous or serrated upon the two opposite sides ; margins 

 with a mucronate extension from each cellule ; or of similar foliate 

 forms united rectangularly by their longitudinal axes, and fur- 

 nished on their outer margins with similar cellules or serratures, 

 the whole supported on a slender radicle. 



These bodies which usually appear upon the stone in the form 

 of simple leaf-like expansions, may possibly have been attached in 

 groups to some other support ; but the form of some of them, and 

 the character of the projecting radicle at the base, indicates that 

 we have the entire frond. These forms furnish perhaps the best 

 illustration of all the Graptolitideoe, of the lesser development of 

 the cells at the base, and their gradual expansion above, until 

 they reach the middle or upper part of the frond. Many of them 

 diminish from the centre upwards, and rarely the cells are more 

 developed above the centre, reversing the usual form, and leaving 

 the narrower part at the base. 



Payllograptus typus. 



Description. — Frond elliptical, elongate-ovate or lanceolate, 

 broad-oval or obovate; margins ornamented by mucronate points; 

 serratures closely arranged, about twenty-four, rarely twenty-two 



