158 THE MEDALS OF CREATION. Cuap. VIL 
subcylindrical, and the external surface covered with the 
rhomboidal scars formed by the attachment of the leaf- 
stalks, and which are widest in their transverse diameter. 
There are two species, which are readily distinguished by 
the form of the stems, and the difference in the size of the 
cicatrices left by the petioles. 
The most common kind is short, and spheroidal, and 
the leaf-scars are relatively large ; its shape has caused it 
to be named “ Crows’ nest,” by the quarrymen, who believe 
these plants to be nests that were built by crows in the 
trees of the petrified forest with which they are imbedded. 
The specific name (nidiformis) adopted by M. Brongniart, 
expresses this popular notion. 
Lign. 50. represents a fine example from the Portland 
Dirt-bed, which exhibits a structure altogether similar to that 
which characterizes the stems of recent cycadeous plants ; 
namely, (a) a central mass of cellular tissue surrounded 
by circles of laminated ligneous rays or plates (6); then a 
zone of cellular tissue (c), and an external cylinder of false 
bark (d). The mode of increase by buds, from germs in 
the axille of the petioles, as in 
the living plants, is also distinctly 
seen. 
The other species is subcylin- 
drical, and the leaf-scars are much 
smaller and more regular than in 
M. nidiformis, indicating a more 
Lien. 51. delicate foliage, as expressed by 
Dye nN AS Dr. Buckland’s specific name: that 
(Guraute: danas. Bd.) of M. Brongniart refers to the 
Wealden. Petrified Forest of the cylindrical form of the stem. This 
sation % plant was higher and more slender 
than its associate. Numerous buds are seen in the axille of 
the petioles in the specimen figured. 
