ESCHARIDvE. 77 



tinguished from its congeners by the entire absence of anything like an avicularian organ. 

 The fragments in which it occurs, however, are so small and so much worn, that its true 



characters must be regarded as still doubtful. 



Genus 5. HEMESCHARA (n. gen.}. 



Polyzoarium foliaceum, contortum sen lamellosum, e strato simplici cellularum quincun- 

 cialium compositum. 



Polyzoarium foliaccous, contorted, or laminar, composed of a single layer of cells dis- 

 posed quincuncially, and opening on one surface. 



SEMIESCHARA, SEMIESCHARIPORA, and MULTESCHABIPORA (pars), D'Orbigny. 

 LEPRALIA (sp.), Busk, Brit. M. Cat. 

 ESCHARA (pars), Auct. 



There are a certain number of Escharidos which, from their peculiar conformation, 

 appear to merit a distinctive generic appellation. In some respects approaching Membra- 

 nipora and Lepralia, they differ from those genera in the circumstance that the poly- 

 zoarium is not adnate by its entire surface to a foreign body ; whilst from Escliara, 

 Melicerita, and Bijlustra, they are distinguished by its being constituted of only a single 

 layer of cells, the polyzoarium forming a continuous thin lamina, on one surface of which 

 the cells open, whilst their backs are exposed in the other. The lamina is often turned 

 back, as it were, upon itself, so as to enclose a cavity which communicates with the exte- 

 rior by two or more contracted openings ; but sometimes it would seem to be more 

 expanded, and variously contorted and laminated, whilst in other cases, again, it assumes 

 an arborescent form, consisting of a hollow cylindrical stem and branches. 



In the formation of the cells themselves, the species thus associated may be sub- 

 divided into two sections, corresponding with Membranipora and Lepralia. In one of 

 these sections the front of the cells, as in Membranipora, is for the most part open, and 

 surrounded by a raised border ; whilst in the other the cells are entire and convex in 

 front, as in Lepralia and Eschar a. Among recent species, an excellent type of the latter 

 section is presented in L. marionensis, Busk (' Brit. M. Cat.'), and of the former, nume- 

 rous (perhaps too numerous) instances will be found in the ' Paleontologie Frangaise.' 



Of the tubular, arborescent forms, at least one living instance exists, though appa- 

 rently as yet undescribed ; and of fossil, two may be cited, SemiescJiara cylindrica and S. 

 arborea, of D'Orbigny (1. c. pi. dccx). 



One species only, referrible to this genus, occurs among the Crag fossils. 



