SIGILLARIA. 169 



or distant, hexagonal, all the angles, except the lateral, being 

 usually more or less rounded. Central vascular print small ; prints 

 of the parichnos larger, crescentic or straight. A small print often 

 occurs above the leaf-scar. Bark smooth or ornamented. 



Leaves linear -lanceolate or elongate linear, uninerved. Cone 

 (Sigillariostrobus), rhizome {Stigmaria in part). 



Anatomy of the stem. Pith well marked, parenchymatous. 

 Centripetal primary wood forming a continuous ring or composed 

 of separate bundles, crenulated at the periphery, consisting of 

 scalariform or reticulated tracheides, with small spiral tracheides 

 forming the protoxyleni groups. Leaf- traces arising in the bays 

 or indentations at the periphery of the primary wood. Secondary 

 wood centrifugal, forming a continuous ring, as in Lepidodendron, 

 consisting of scalariform tracheides pitted on both the tangential and 

 radial surfaces. Cortex differentiated into two or more zones, the 

 outer consisting of thick -walled periderm. 



The Sigittaria are divided into two main groups, the Eusigittarice, 

 with ribbed stems, and the SubsigiUarice, without ribs. Further 

 subdivisions bave been proposed, and while it is now known that 

 these are without taxonomic importance, certain names are still 

 sometimes used to denote a particular type of stem-cast. Thus 

 the SubsigiUarice, the group to which the specimens described here 

 belong, have been divided into two subgroups. The Clathrarice 

 include stems in which the leaf-scars are placed on contiguous, 

 rhomboidal cushions, usuallv somewhat elevated, the cushions being 

 separated by well-marked oblique furrows. In the Leiodermarian 

 type there are no leaf-cushions, the leaf-scars being distant and 

 separated by bark, which is ornamented in various ways by stria?. 

 Both these types may occur on the same specimen, as in the 

 case of Sig Maria Brardi, which is found in South Africa in 

 association with Glossopteris. 



Sigittaria first appears in the Lower Carboniferous, but is neither 

 very abundant nor represented by many species in these rocks. 

 The genus reaches its maximum in the Upper Carboniferous. In 

 the Permian it is less frequent, and probably dies out at the end 

 of that period with the exception of one species which is known to 

 persist into Triassic times. 



