8 
CRETACEOUS BEACIIIOrODA 
The uumher of radiating ribs is very variable. The typical form from Ignaberg 
is distinguished by its usual roundly sub(|uadrangular form and numerous subequal, 
or alternately shorter and longer, and tliicker and thinner ribs, being 38-dG in 
number. This form is common in the Baltic Chalk, and it also occurs at Maastricht, 
though apparently rarely. The two as yet known South Indian examples agree well 
with this typical form, except that the ribs are slightly fewer in number. Specimens 
from Folkstonc arc similar in form, but have still fewer ribs. 
At Maastricht another variety is more common ; it has a more distinctly rounded 
shape, the ribs arc either numerous, or they arc few (21-28 only), and thick. This 
latter form has been designated as var. iKmcicostala l)y Bosquet, and some speci- 
mens of it are wider than long, Avhilc in typical Ljnahergensis the opposite is the 
case, or at least the two diameters arc equal. A third variety is figured by 
Schloenbach (loc. cit., pi. xl , fig. 21), wliieh has the numerous ribs of the type form, 
but is more rounded in shape than the last ; the two valves arc nearly equally 
elevated, or the neural is even a little higher than the hmmal. 
There arc besides two other varieties indicated by Schloenbach. The one, 
C. slvLv, Kunth, fairly agrees with the last mentioned variety, and the other includes 
specimens figured by Davidson and Deslongchamps, attached by a broad surface 
of the neural valve. 
C. is found in England in the U])pcr and Lower Chalk ; on the con- 
tinent of Europe it occiu's in the uppermost cretaceous deposits, — Danien and 
Senonien of d’Orbigny, AVeisse Kreido and Oberer Phener, — from Xorway all 
through G('rmany, Belgium, Bohemia, and Prance. 
LocaUty. — Olapaudy ; only two specimens have as yet been found in a broAvnish 
oolitic rock. 
Forma (ion. — Arrialoor group . 
Family —RIIYNCHONFLLID.F. 
The animal of Fliynchonelkti the only genus knoAvn in a recent state, is either 
free, or attached to sub-marine objects by a muscular pedicle situated at the beak 
of the neural A'alve ; tho arms arc spiral, fleshy, srqiportcd only at their base by 
short shelly processes ; the musevdar system consists of a strong adductor, divided 
dorsally into four branches and veutrally united into one ; besides that, the usual 
cardinal and retractor muscles of tho peduncle arc present, but the latter is some- 
times obsolete, in Avhieh case the retractor is equally so ; tho mouth is situated in 
the middle of a membrane, separating tho small posterior visceral part from the 
anterior respiratory cavity ; the alimentary canal passes through the notch of the 
hinge-plate and ends behind the point of insertion of tho adductor near the centre 
of the neural valve ; the pallial veins originate in four much sub-divided branches ; 
the mantle is not attached to the shell, and its margins arc provided with more or 
less numerous, fine, chitinous setse. 
The shells arc inequivah'e, very variable in shape and size, of fibrous or pyra- 
midal, not punctate structiu’c ; tho two valves arc articulated by a pah of hinge- 
