8 JURASSIC RHYNCHONELLIDS 
Ager (1965a) suggested that the strongly uniplicate rhynchonellids such as 
Homoeorhynchia acuta and Rhynchonella loxiae were characteristic of sand grade, 
sublittoral sea floors. However, it is not thought that all species of the genus 
Rhynchonella lived in this type of environment as at least two of them, namely, 
R. subvariabilis and R. rivelensis, occur in clays or marls. It appears from the 
relatively limited information available that the earlier species attributable to 
Rhynchonella s.s. are always found in such lithologies and that it is not until Volgian 
times that the genus is found in a more sandy facies which presumably represents a 
higher energy environment. Makridin (1964), who gives the range of Rhynchonella 
as late Kimmeridgian—early Cretaceous, states that, ‘‘ members of the genus are 
most widespread in the shoaly facies of a sandy and sandy-clay sublittoral’”’. If the 
above information is correct, then it is interesting to note that the genus became 
much more morphologically diverse on colonising the higher energy environment. 
It is possible that Riynchonella only colonised these environments on the extinction 
of such genera as Septaliphoria. In order to account for the occurrence of R. 
subvariabilis, Ager suggested a pelagic mode of life and it is thought that such a 
mode of life would also best account for the occurrences of the earlier species of the 
genus such as R. rvivelensis and R. triplicosa, this is discussed further below. 
(b) Sea floors in the vicinity of reefs. 
While Ager (1965a) referred exclusively to the forms encountered in the vicinity 
of hermatypic coral reefs, within the Upper Jurassic, it is possible to subdivide this 
environment according to whether the reefs are coral or sponge. The greatest 
development of sponge reefs is found in the regions of Swabia and Franconia where 
they flourished from middle Oxfordian to, at least, lower Volgian times. The 
rhynchonellid fauna associated with these reefs is very distinctive and consists almost 
entirely of species of the genus Lacunosella. The incidence of sponges with Lacuno- 
sella spp. is such as to suggest that the rhynchonellids were actually dependent on 
them. Middlemiss (1962) has recorded rhynchonellids within the folds of Rhaphi- 
donema in the Lower Greensand at Faringdon, Berkshire, and this may possibly be a 
commensal relationship ; unfortunately, details of the rhynchonellids were not 
given. It has also been suggested (Ager, 1965a) that Orbirhynchia of the Upper 
Cretaceous adopted a similar mode of life and it may be significant that both the 
latter genus and Lacunosella possess the distinctive blade-like falcifer crura. Apart 
from Lacunosella, the only other rhynchonellid genera known to occur in the sponge 
reef facies are Acanthorhynchia (Echinirhynchia) and Monticlarella ; these may well 
have been pelagic forms and are discussed further below. 
The important factor in determining the distribution of the lacunosellids would 
seem to be the presence of sponges and whether these were living as reef assemblages, 
loose groups or “lenses’’ mattered little. While the greatest abundance and 
variety of lacunosellids is found in the sponge reefs of Germany where sponges were 
the dominant feature of the fauna during the Upper Jurassic, in the southern French 
Jura L. avolica occurs in calcareous shales with only isolated sponges. 
The areas around the coral reefs appear to have been colonised by two genera. 
The more distinctive externally is Torquirhynchia gen. nov., which comprises a 
