ESCIIARIDjE. 69 



that these processes are avicularia. From their position and form, they are very charac- 

 teristic of the species, even where most of the other characters are obliterated. No 

 ovicells, like those in most other polyzoa, appear to exist in E. monilifera ; but intermixed 

 irregularly among the common cells, there will be observed iu many specimens, though 

 not in all, large openings, of a quadrangular form, four or five times the size of the 

 mouths of a cell, and occupying in fact the entire front of a cavity at least twice the 

 dimensions of a common cell. These openings are usually patent, but in many instances 

 they are closed by a cribriform calcareous plate, and have below them a curious bracket- 

 like shelf, at the upper angles, of which on either side may be noticed in some cases the 

 traces of minute avicularia corresponding to those on each side of the mouth in the other 

 cells. These peculiar cells, the " accessory cells " of D'Orbigny, may probably be taken, 

 as before said, to represent the fertile cells of E. monilifera. One is represented, covered 

 in by its cribriform plate, at a fig. 2, plate XI. 



Very considerable differences of appearance in this Eschara are produced by age. In 

 the older cells, as remarked by M. Edwards, the mouth, without much change of form, 

 becomes immersed, and finally altogether filled up ; the pores also are obliterated, and the 

 surface appears solid, either marked by the ridges indicating the situation of the cells, 

 or nearly smooth, with only indistinct undulating lines, more like those on the surface of 

 a piece of a Corallium, than of the skeleton of any Polyzoon. 



Genus 2. MELICERITA. M. Edwards. 



Polyzoarium explanatum, e cellulis quincuncialibus in utraque superficie et in seriebus 

 transversis dispositis compositum. Lamellis conjunctis. 



Polyzoarium composed of cells disposed quincuncially on both surfaces in transverse 

 series ; the two layers inseparable. 



MELICEIUTA, M. Edwards, Sur 1. Eschares foss., p. 25. 



MELICERTINA, Ehrenb. 



ULIDIDM, S. Wood, Ann. Nat. Hist., xiii, p. 17. 



The distinction between this genus and that of Eschara, to which it is very closely 

 allied, was first indicated by M. M. Edwards, who observes (1. c.) that the " mutual 

 relation of the cells is essentially different from that which obtains in the latter genus." 

 In Eschara each cell produces at its superior extremity another cell, so that the aggregate 

 growth is eventually made up of parallel longitudinal series, the cells in the contiguous 

 series being for the most part regularly alternate, and having their longitudinal axis 

 coincident with that of the series to which they belong ; the only interruption to this 



