170 GUIDE TO THE FOSSIL INVEllTEBRATE ANIMALS. 
Gallery of Huleoatcphaims '(voiw Wm IVn llaiidiaii near Moscow, sliowiiig 
W^/case ividesceiit shell, 'i'he large Holcodciihanui^ iind the 
0 _ still larger rerisphinrtes (/if/anfctin, from the I’ortlaiul Stone 
of England are in the AVall-case. A small si)ecimen of the 
latter species had the shell turned into silica, and the inlilling 
limestone has been dissolved out, exposing the shape of the 
septa and the position of the siphuncle. 
Wall-case The Lower Cretaceous rocks have not furnished many 
ammonites, but the large ramlioplileH Dcslwycsi from the 
Lower Greensand carries on the general plan of the genera 
just mentioned. Other new genera appear in the series from 
Table-oases the Albian of Kscragnolles (Var), and i'rom the coaeval Gault 
10 , 11 , & 12 . p’olkestone. The iridescent appearance of these and other 
ammonites ])reviously noticed is due to the solution of the 
outer layers of the shell, by which the inner nacreous layers 
are ex])osed. Here we meet with Hoplites, characterised by 
a broad groove on the outer margin of its shell, similar to 
that previously seen in the otherwise unlike Hchlolhcimia of 
the Lower Lias and ParJdnsojiia of the Lower ( )olites. The 
specimens of this genus from Folkestone form a series 
illustrating the decline of ornament from tuberculate, 
through ribbed, to smooth. Similarly Mortoniccras shows a 
decline from highly tuberculate to ribbed. ]\[. rostratam marks 
Wall-ease a wide-spread horizon in the All)ian, and there is a splemlid 
.series of it from both Gault and Upper Greensand, preserving 
the long rostrum at the .shell-aperture. rhijUoccras Guettardi 
and several species of Jfolcodisrii.s show periodical constric- 
Table-case tions of the shell-aperture. The specimens from the Cam- 
bridge Greensand are derived from the underlying ( Jault, and 
those from the Led Chalk seen in the next ca.se are also of 
that age. 
Table-cases The Cenomanian forms in the Table-case include 
12 & 13 . characteristic Mctacanthoplites rol oinagcnsis from llouen, 
Brahmaites from Pondicherry, and Fachydiscus from various 
European localities. The Upper Cretaceous rocks ol South 
Dakota yield specimens of Flacenticeras with elaborate 
sutures. Tissoiia, on the other hand, from the Senouian of 
jVlgeria, shows that return to a Ceratite form of suture which 
is found in many late Cretaceous ammonites. Among the 
British specimens from the Chalk Marl and Chalk are many 
iigured in 1). Sharpe’s monograph published by the Palaeonto- 
graphical Society. Those from the Chalk Marl include a 
tine series of Schloeiibachia ranging from the tuberculate 
Schlocnhachia Oonpei, through the more or less rilibed 
