o/" Ulodendron to Lepidodendron, &g. 173 



cular organs, which stand out in some relief, are about | inch 

 long and nearly as broad, and appear to have had rounded 

 apices. The fourth and uppermost appendicular organ is not 

 well shown, being partly covered with the matrix. From 

 the presence of the foliage, the form of the leaf-scars cannot 

 be seen. 



Specimen No. 19. From the bituminous Oil Shales, Straiton, 

 near Loanhead, Midlothian (Calciferous Sandstone Series). 



This specimen is a portion of a branch about 1 foot long 

 and 3 inches wide. It shows a vertical row of twelve TJloden- 

 droid scars, and is mainly interesting as partly exhibiting the 

 true outer surface of the stem, in which occur a few longi- 

 tudinal clefts. 



III. Geneeal Conclusions. 



The point in which lies the essential generic difference 

 between Lepidodendron^ LepidopMoios, Sigillaria, and Rhyti^ 

 dodendron is the form and structure of the leaf-scar. My 

 apology for referring to the generic characters of three such 

 well-known genera as Lepidodendron^ Lepidopliloios ^ and 

 Sigillaria is that their generic differences form the basis of 

 my subsequent remarks. I am aware that, in addition to the 

 structure of the leaf-scar, there are other points of minor 

 importance which enter into the definitions of these genera ; 

 but as far as the subject which specially occupies our atten- 

 tion at present is concerned, we shall not require to enter 

 more fully into the generic differences of the above-mentioned 

 four genera other than those characters derived from the struc- 

 ture of the leaf-scar, the mode of the attachment of the leaf 

 to the scar, and the cortical extension on which, in some cases, 

 the leaf-scar is supported. 



These four genera may be briefly defined as follows : — 



Lepidodendeon. (PI. VII. fig. 15.) 



Leaf-scars contiguous or distant, rhomboidal or fusiform j 

 consisting of a "j?eTc?"(c) and vascular-bundle scar (a), which 

 is usually situated towards the upper part of the field. The 

 vascular-bundle scar is transversely rhomboidal, its upper and 

 lower angles rounded, the lateral angles more or less promi- 

 nent. Vascular-bundle cicatricules three^punctiform {J)). Im- 

 mediately beneath the vascular-bundle scar are two small 

 oval pits {d)j one placed on each side of the median line (_/)* 

 Above the vascular scar and on the medial line is the " ligule " 

 depression (e) . Leaf-hase attachtd to the whole area of the 

 leaf -scar {including the '"'•field''''). 



Ann. & Mag. N. Hist. Ser, 5. Vol. xvi. 13 



