Notices of Memoirs — Prof. Setcard — Floras of the Past. 555 



impression,'^ though shallow, is here well marked and about 13-5 mm. 

 wide, but this may have been much narrower or even have entirely 

 disappeared on the body-chamber, so that the transverse section of 

 the body-chamber may have been more nearly digonal. Fortunately 

 in the present specimen a few of the septa are visible, or at least 

 partially visible ; near the anterior end of the specimen th"By are 

 about 6'Omm. apart; they are, however, best displayed at about the 

 commencement of the last third of the outer whorl, i.e. where 

 the specimen is 69 mm. in diameter ; here they are seen on 

 a portion of the peripheral area and on a part also of the side of 

 the whorl ; on the lateral area they form a very slight backwardly- 

 directed curve, and, crossing the umbilical rim, traverse the peripheral 

 area in almost a straight line, or with only a very feeble backwardly- 

 directed curve ; on the periphery they are about 7-0 mm. apart. 

 So far as can be seen, the form of the septation closely resembles 

 that of Vestinautilus pinguis as figured by Dr. Foord,^ but the 

 chambers are a little shallower than shown in that figure. Notwith- 

 standing the characters which differentiate this specimen from Foord's 

 figured example, viz., the greater convexity of the peripheral area, 

 the narrower and deeper hyponomic sinus, and the relatively 

 greater height of the whorl in proportion to its width, there can 

 be no doubt that the two forms are very closely allied and most 

 probably specifically identical. In referring his species to the 

 genus Vestinautilus, Dr. Foord seems, therefore, to be correct, the 

 form of the septal sutures supporting that conclusion. 



isroTiciES oip :vnE3vnoi:RS, etc. 



I. — Floras of the Past : their Composition and Distribution, 

 By A. C. Seward, F.R.S., Fellow and Tutor of Emmanuel 

 College, Lecturer on Botany in the University of Cambridge. 



[Continued from the November Number, p. 512.) 



THE geographical distribution of plants of af)proximately 

 Rhsetic age is shown in the following table on p. 557, which 

 demonstrates an almost worldwide range of a vegetation of uniform 

 character. The character of the plant-world is entirely different 

 from that which we have described in speaking of the Palgeozoio 

 floras. Gymnosperms have ousted Vascular Cryptogams from their 

 position of superiority ; ferns, indeed, are still very abundant, but 

 they have undergone many and striking changes, notably in the 

 much smaller representation of the Marattiacese. The Palseozoic 

 Lycopods and Calamites have gone, and in their place we have 

 a wealth of Cycadean and Coniferous types. As we ascend to 

 the Jurassic plant-beds the change in the vegetation is comparatively 

 slight, and the same persistence of a well-marked type of vegetation 



1 The ' zone of impression ' or ' impressed zone ' is the zone which is in contact 

 with, and impressed by, the peripheral area of the preceding whorl. 

 ^ Op. jam eit., pi. xxv, fig. 3a. 



