256 Mr. J. Lycett on the Fossil Conchology of the 



spiral univalves which it is possible to imagine. The Rostrotremae, 

 though rare, are likewise represented by five species. We seem 

 in fact to have a repetition of the circumstances under which the 

 mollusca of the Great Oolite lived and multiplied. In a former 

 paper we alluded to an almost entire absence of the Cephalopoda 

 which distinguishes our Great Oolite, and it would appear that 

 this feature likewise extends to the same formation throughout 

 France. Thus Archiac does not mention a single species in the 

 district which he has illustrated, and Deslongchamp is equally 

 silent in describing the Normandic fossils. The " Fimbria bed," 

 in striking contrast to the other portions of the Inferior Oolite, is 

 distinguished by a similar paucity of Cephalopoda ; hitherto only 

 a single specimen of Ammonite has been placed in our cabinet, 

 and we have searched in vain for a Nautilus or Belemnite. There 

 are several Terehratula, of which the T.jimhria is the most 

 abundant ; the varieties of figure and markings which this shell 

 undergoes in its stages of growth become interesting when placed 

 beside a similar series of the recent T. AustraliSy which it very 

 nearly resembles in every circumstance. Of the fossil species 

 but few will be found to have attained the characters of old age, 

 and these latter are rarely equal in size to those which died on 

 attaining middle life, a fact of which some striking examples may 

 be cited in certain recent shells. As the T. Australis, unlike the 

 Brachiopoda generally, is found in water only knee-deep near 

 Sidney, we may be allowed to consider it probable that the Tere- 

 bratula and other shells of the Fimbria bed were likewise deni- 

 zens of a shallow sea ; such a condition would assist in explain- 

 ing the absence of Cephalopoda and the general resemblance 

 to the association of Great Oolite shells. As a last resemblance 

 a general dwarfing of species may be noticed, some examples of 

 which will subsequently be given. This general resemblance 

 however extends but in a very limited degree to specific identity : 

 thus, of the seven Nerinece, one only is common to both ; the 

 Cerithia are altogether difi'erent, as are likewise the Chemnitzias 

 and Cylindrites. Our collection from the Fimbria bed contains — 



59 Univalves and Radiaria, of which 22 are Great Oolite species. 

 72 Bivalves, of which .... 29 are Great Oolite species. 



131 51 



Thus only about 38 per cent, of the whole are common to both 

 formations. On passing downward through the freestones these 

 shells rapidly disappear, and on arriving at the lower rag- stones 

 another and very dissimilar suite predominate ; the profusion of 

 Nerinea has entirely vanished, and equally in vain might we look 

 for a Cerithium or a Rostrotrema, and we very rarely meet with a 



