1848.] LONSDALE ON FOSSIL ZOOPHYTES. 71 



plate was occasionally detected, agreeing with those fully exposed in 

 the vertical slice of a branched specimen ; while the absence of such 

 a lamma in many cavities only accords with what frequently occurs 

 in fossil Anthozoa, and has even led to a statement of their total 

 absence. Again, in one portion of the coral zone a cellular structure 

 was clearly shown between the visceral hollows, and distinguishable 

 from intersected tubes by irregularity of form, and more or less 

 marked approach to the arrangement of the layers in other slices. 

 Still further, in a vertical translucent section was noticed an overlying 

 or unconformable development, perfectly resembling those so abun- 

 dant in the parasitic section. 



The surface-characters varied according to the amount of preser- 

 vation, and the state of development at the time of the animal's de- 

 struction. Respecting worn conditions no remarks are necessary ; 

 but attention must be solicited to variations due to different states of 

 growth. The whole surface occasionally exhibited an irregular net- 

 work, and the apertures of the abdominal cavities could not alwa3^s 

 be easily separated from the cellular composition. This indistinct- 

 ness was ascribed to the specimen having lost its vitality while a 

 cellular layer was forming, and the upper laminae of the cells had not 

 been produced. In cases of a tolerably preserved, mature surface 

 (fig. 11), the larger openings had a raised, bold rim, but the second- 

 ary were small, sometimes almost inconspicuous, and depressed. It 

 will be shown in a subsequent paragraph, that layers separated me- 

 chanically exhibited similar characters, proving that the condition 

 last-mentioned indicated a periodical perfecting of composition. 



Among the internal structures, the abdominal cavities first claim 

 attention. Their great uniformity of dimension and considerable 

 range, as well as slight divergence in the axis of the branch, with a 

 sudden, almost horizontal course in the outer zone, were well-shown 

 in vertical sections (fig. G) ; and similar characters were clearly 

 deducible from transverse slices (fig. 9, 10). The simple cross- 

 laminse were very often wanting, as already stated, but they occurred 

 in sufficient number to prove, that they formed one of the essential 

 structures of the coral. The interspace between the plates was va- 

 riable, but always considerable and unoccupied (fig. 6*) ; and no 

 marked diiference was noticed between the laminae and intervals of 

 the axis and those of the outer zone (fig. 6). There was no accord- 

 ance in position in adjacent cavities (fig. 6*) ; and when the range 

 agreed with that of the upper or lower lamina of a concentric layer, 

 the coincidence was evidently accidental. Similar transverse laminae 

 with clear interspaces are well known to occur in the recent Heliopora 

 ccendea and Pocillopora damicornis ; also in Favosites GotJdandica 

 and many other extinct corals ; but always with an aggregate of struc- 

 tures diiferent from that of Choristopetalum impar. In polished, opake 

 sections the boundary of the cavities appeared to be thick, and those 

 of adjacent cavities united ; but in translucent slices, the thick wall 

 was shown to have a complex texture, which became markedly cel- 

 lular, where the intervals between the abdominal hollows increased ; 

 and even in llie central axis the boundaries were divided by a fine, 



