A. C. Seward — Variation in Sigillaria?. 217 



simply different conditions of one and the same plant, yet there are 

 certain distinctions and constant characters which must keep us on 

 our guard against uniting as one species what are really distinct 

 forms. One of the examples cited in illustration of this is 

 S. Moureti, which suggests a very close relationship with S. Brardi ; 

 it is distinguished, however, from S. Brardi by the complete absence 

 of an indentation on the upper edge of the leaf-scars, by the higher 

 position which the cicatriculae occupy on the leaf-scars, and by the 

 round form of the lateral cicatriculse placed somewhat above the 

 central or vascular bundle cicatricula. 



As further illustrating the variations in size of the leaf-cushions 

 and leaf-scars on one and the same specimen I may add a few notes 

 on three specimens which I had the opportunity of examining last 

 year in the museums of Berlin and Breslau. 



1. Sigillaria of Rhytidolepis type from the Coal-measures of Alte- 

 nessen ; in the Bergakademie Museum, Berlin. This specimen 

 serves to show the differences in the size of the leaf-scars, the 

 variation in breadth of the furrows and in the distances between 

 the scars. Four ribs shown, three rows of leaf-scars. Breadth 

 between ribs 1 & 2 = 3cm. ; between ribs 2 & 3 = 2"3cm. Length 

 of leaf-scar between ribs 1 & 2 = 9 mm. ; breadth of ditto = 1*2 mm. 

 The distance between the leaf-scars in the first furrow, i.e. between 

 ribs 1 & 2, varies from 1*1 cm. to 1*3 cm. Length of leaf-scar 

 between ribs 2 & 3 = 1cm.; breadth of ditto = 8 mm. The leaf- 

 scars in the third furrow, i e. between ribs 3 & 4, correspond closely 

 with those in the second furrow. The specimen agrees closely with 

 S. principis (Weiss) and S. laevigata (Brongniart). 



2. Sigillaria from Coal-measures of Bochum ; in the " Goeppert 

 Collection," Breslau University Museum. Length of stem, 28 cm. : 

 average breadth = 6 cm. Details not very clear. At the upper 

 end the leaf-scars and cushions are of the Ehytidolepis type ; the 

 distance between these leaf-scars = 3 to 4 mm. Breadth of leaf- 

 scar = 3-5 mm. ; length = 3-5 mm. 



Passing down the stem the leaf-scars rapidly get closer together, 

 until they are almost contiguous, showing a passage from a Rhyti- 

 dolepis to a Favularia type. Towards the lower end of the specimen 

 are indications of vertical fruit-bearing scars, below this the leaf- 

 scars become farther apart again. Zeiller 1 figures a specimen 

 showing a somewhat similar case of variation in the distances 

 between the leaf-scars (S. Sauveuri, Zeiller). 



3. Sigillaria. Specimen in the " Goeppert Collection." 



The leaf-scars of the upper part have a breadth of 4-5 mm., and 

 a length of 2 mm. ; on the lower part the leaf-scars have a breadth 

 of 2*5 mm., and a length of 2 mm. The former agree closely with 

 /S. microrhombea (Weiss), 2 var. nana, the latter with S. cancriformis 

 (Weiss), vars. Paulina and S. acarifera. 



1 he. cit. pi. lxxxiv. fig. 1. 



2 For figures of Weiss's species, v. " Die Sigillarien der Preussischen Stein- 

 kohlengebiete," Abhand. zur Geolog. Special-Karte von Preussen und den 

 Thiiringischen Staaten, Band VII. Heft. 3, Taf. vii. and xiv. 



