the Genus Eschara. 173 



which inhabit the seas in which the transition limestones were 

 formed, we know of no well established example of a polypidom 

 belonging to that family ; it is even probable, that at that re- 

 mote period very few polypi of the order Bryozoaires existed, 

 whilst Alcyoniae and Zoanthaircs, whose structure is much more 

 simple, abounded. The Escharae are rare in the Jura formation, 

 but in the chalk and tertiary limestones their number is propor- 

 tionally greatly increased; and in the more recent series, by some 

 geologists denominated quaternary or pliocene strata, the quan- 

 tity of the remains of these polypi much exceeds that of those 

 fossils belonging to less elevated orders, such as the Zoantha- 

 ires and Alcyonae. 



The Eschara, properly so called, first appear to have existed 

 about the time of the formation of the Jura limestone of Caen ; 

 and Lamouroux has in fact found in this deposit a fossil which 

 undoubtedly belongs to this genus ; and Desmarest has shewn 

 that there is a second. In the chalk of Maestricht these poly- 

 pidoms are by no means rare; and the number of species 

 figured by M. Goldfuss, as belonging to this geological for- 

 mation, amounts to ten ; but, as will presently be seen, all the 

 fossils arranged by this author under the name of Eschara do 

 not appear to have a legitimate claim to remain in this group ; 

 and it also appears highly probable that simple modifications 

 dependent upon age have, in more cases than one, been regard- 

 ed as constituting specific differences, and so have led to the 

 improper multiplication of species. In consequence of this, his 

 list of the Eschara of the chalk formation will be very con- 

 siderably reduced ; but, on the other hand, it will be augment- 

 ed by new species which I mean to propose at the close of this 

 memoir. The tertiary strata about Paris and those of West- 

 phalia, have likewise furnished Messrs Desmarest and Goldfuss 

 many Eschara?, but unfortunately few of these fossils have 

 been represented in such a way as to allow us to come to any 

 satisfactory conclusion. We, too, have met with some species 

 which belonged to this geological epoch, and which appear to 

 us to be new ; but it is especially in the English Crag and the 

 analogous deposits in the basin of the Loire, that we have found 

 the greatest variety of these polypidoms : up to the present 

 moment no naturalist has described one of these, and the num- 



