64 



THE CRAG POLYZOA. 



slender as, except on careful inspection, to appear cylindrical. A transverse fracture, 

 however, will, in doubtful cases, show the median plane parting the two layers of cells, 

 and distinguishing any form of Eschar a from a Vincularia or SaUcornaria. 



The cells in Eschara are of the open, urceolate form, decumbent, and generally con- 

 fluent. In most cases they are of uniform character throughout the growth, but in 

 some instances those at the margin of the branches or lobes differ from the others. 

 Many, if not all the Escharee, are furnished with avicularian organs, which are either 

 situated in some part of the cell itself, or are what may be termed intercellular, replacing, 

 in fact, one of the ordinary cells ; and this appears to have been a frequent condition in 

 the older fossil forms. In most Escharce ovicells of the usual kind are met with, but in 

 some these organs appear to be replaced by cells very different in form, and of far larger 

 dimensions than the ordinary cells, and which are in some cases widely open, and in 

 others closed in front by a cribriform calcareous plate. These larger cells, which have 

 been termed by M. D'Orbigny " accessory cells " (cellules accessoires), were by that 

 observer supposed to represent the habitations of male polypides ; but as this explanation 

 is irreconcileable with all we know respecting the sexual relations of the Polyzoa, it is 

 clearly not admissible. The more probable supposition would appear, as above said, to 

 be, that these are the fertile cells of the polyzoarium. I am unacquainted with any living 

 Escliara furnished in this way, but it may be remarked that a very similar provision exists 

 in the genus Selenaria, B., one of the living Lunulites. 



The genus seems to have made its first appearance in the Jurassic period, to have 

 been tolerably numerous in species in the Cretaceous and Tertiary, and probably at 

 present to be still more prolific in species than at any former peiiod, although, as remarked 

 by M. Edwards, no fossil species has been clearly identified with one now existing ; the 

 Eschara foliacea of Michelin ('Icon. Zoophyt.,' pi. xiv, fig. 9) clearly not belonging to 

 that species, if an Eschara at all. M. D'Orbigny remarks, that all the Escharce of the 

 Cretaceous period have the walls of the cell imperforate, whilst in the Tertiary and more 

 recent forms they are usually perforated. 



SYNOPSIS OF SPECIES OF ESCHARA (Fossil in the Crag). 



(a) Foliaceous. 



1. E. pertusa 



2. E. incisa 



3. E. porosa? 



4. E. sinuosa 



5. E. cormita 



(6) Lobate or ramose. 



6. E. Sedgwickii . 



7. E. monilifera 



p. G.->, PI. X, fig. 2. 



p. 65, PI. X, fig. 3. 



p. 06, PI. XI. fig. 4. 



p. 66, PI. X, fig. 6. 



p. 67, PI. VIII, fig. 5 ; nd PI. X, fig. 5. 



p. 67, PI. X.fig. 1. 



p. 68, PI. XI, figs. I, 2, 3. 



