FIB8T, OB PSIL04 BEAU BRAN< II 121 



FlHST \n:> m .■ "M> Si BS1 B 



I'siloceras plauorbe, Htatt. 



\ ul leve. 

 Plata i > ■- I ' Nob i'i. \i n ( i : i i \n i 



Amm planer' - I \ 



u .. .. .1 . ; .- \ - i .11 



' ■ ! I ' 



Amm 



... I 



W S mar, Radern, Ni I '■ (Ten > 



This remarkable form ia a somewhat flattened discoidal and perfectly smooth 

 . in its typical adult form. The young arc often plicated. 



\ m: plicatum. 



|-Ul. II, -in. I. ii. PL D I I* S. 



Amm Q 1 S Jura, pi. i Bg 1-14 



Thia shell differs from varietj ; '" merely in having immature pilsa or folds in 

 the ueologic and ephebolic stages. There is therefore the most gradual and 

 hardly perceptible gradation from the preceding variety to this form. The Bepta 

 eedingly variable. The marginal digitations maybe either verj 

 shallow, as in the Arietidas generally, or thej may be foliaceous and complicated, as 

 in the radii The lobes and Baddies maj :i 1 ^< » vary exceedingly in size 



and proportions; some species have deep and narrow Baddies with long broad 

 n the radi . while others, more like the typical Arietidae, have 



shallower, broader saddles, and shorter, more pointed lobes In the collection al 

 Semur there are forms from Saulieu identical with the South German, which 

 when compared with tn and Jo) show closei approximations than 



any specimi as seen elsew here. 



B -'"I collection contains undistorted specimens of this species from 



1 nn, and in Dr. Wright's collection from Whitby the pticaim variety i- labelled 



I I '• I nnection with the flattened Wntcbel specimens of 



oul by the large tablet in the British Museum, 



it one hundred and fifty specimens. Of these, perhaps ninety 



exhibit folds like those of pliai The largest on this slab is from 



in diameter. These large specimens are not equivalent I 



■ I supposed, but t<> / / ems to be a dwarfed form 



with the folds often developed verj Btronglj in the young, 1 and the shell has fine 



Plate IX. Fig. 14, ] 5. In the Museum of 

 1 • omplete from /■ •• to vai 



D( J aid in another direction to the var. o from 



Semui ' Thia is a slightly plicated fonn, having 1 1 1 « - sides of the whorls bn 



1 Th«-«« it' i 

 »lw»- 



