On Variatior n of Sigillarice. 43 



That S. diseoidea, Lesq., is simply one of the diverse forms 

 produced by the uniou aud distortion of the geminate vascular 

 scars of 8. reniformis, I have determined by examination of 

 numerous specimens in several collections of coal plants. In 

 the cabinet of Mr. Edward Jones, Olypbant, Pa., there are 

 several remarkable specimens of decorticated 8. reniformis, 

 showing all phases of the transition from the geminate oval 

 s ;ars to the single orbicular scars described by Prof. Lesque- 

 reux. Two large slabs are especially worthy of mention. Each 

 has ten rows of elevated disciform scars, four inches apart and 

 twenty to twenty-four inches in length. The scars are one 

 inch in diameter, almost touching, and are emarginate either 

 above or below, as shown in Prof. Lesquereux's figure of 8. 

 diseoidea. Many of them are emarginate on both the superior 

 and inferior sides; and nearly all have an irregular depression 

 in the centre, or a depressed line — the junction of the two 

 vascular scars. Many of the discs are deeply lobed above and 

 below, and some are entirely divided into two elliptical or oval 

 soars. On one slab, the greater part of two rows thus clearly 

 appear as 8. reniformis. Eig. 1 (Plate III), shows four scars, 

 from different portions of one of these slabs, which fairly 

 represent the general character of the scars and their transi- 

 tion in form. 



Other specimens showing the true nature of 8. diseoidea, 

 so-called, may be seen in Professor J. S. Newberry's collec- 

 tion, New York ; in the Museum of the Wyoming Historical and 

 .Geological Society, Wilkesbarre, Pa.; and in most large col- 

 lections from the Wyoming basin. 



Another specimen of 8. reniformis. in Mr. Jones' cabinet, 

 shows a great variation. The geminate oval scars on one side 

 of the slab are one-half to three-fourths of an inch in length, 

 and are separated by a space equal to one-half the breadth 

 of either scar. But these diminish in size, and gradually 

 coalesce to form single disciform scars, which continue to 

 lessen in size until they become oval or elliptical and only 

 one-fourth to one-eighth of an inch in length. The scars are 

 crowded longitudinally. These rows are only twelve inches 

 long, and every row presents a similar change. Fig. 2 repre- 



