1848.] LONSDALE ON FOSSIL ZOOPHYTES. 69 



ranged in more or less regular rows (fig. 6), which are separable me- 

 chanically with smooth surfaces (fig. 7, 8). Conceiving that these 

 distinctions justify an altered assignment, and not having been able 

 to discover an aggregate of similar structures in any genus known to 

 him, the describer proposes to designate the greensand coral by the 

 term Choristopetalum {yjoptarbs, separahilis, TreraXop, lamina), in allu- 

 sion to the separable layers between the tubes. 



Choristopetalum, n. g. 



Ge?i. char. — Branched or encrusting : surface beset with apertures of 

 two kinds, — one the terminations of tubular, abdominal cavities, — 

 the other smaller and connected with an intermediate cellular struc- 

 ture : abdominal cavities crossed by transverse laminae, no lamellae 

 or furrows ; adjacent tubes more or less distant : interspace occupied 

 by separable layers, perforated by pores : yomig cavities produced 

 between the pre-existing. 



Choristopetalum impar, n. sp. 



(Pl. IV. fig. 5 to 11.) 



Sjaec. cA«r.-— Unequally branched, or encrusting : apertures of abdo- 

 minal cavities raised, — of the cellular pores immersed ; no order of 

 arrangement in the openings, nor numerical proportion between the 

 large and small : abdominal cavities nearly vertical or slightly diver- 

 gent in the axis of the branches, almost horizontal in the outer zone ; 

 distance between transverse laminae variable : interspace dividing the 

 cavities very small in the axis of the branches, often considerable in 

 the outer zone ; composition and range of cellular layers unequal. 



As respects detailed remarks on the series of specimens submitted 

 to examination, the manner of growth primarily demands attention ; 

 and it is best to consider first, the nature of the normal or branched 

 mode. No example was afforded in the collections of a base or of 

 a perfect upper extremity ; but sufficient proofs that the plan of 

 branching varied considerably. One instance exhibited a marked 

 tendency to regular bifurcations (fig. 5) ; another had a principal 

 stem A\ith lateral oif-shoots ; while in some cases it was impossible 

 to reduce the ramifications to any plan. There was also no uniformity 

 in the distance between either the bifurcations or the lateral shoots. 

 The process which attended the branching was not satisfactorily 

 shown in the sections obtained ; but if it was rightly understood 

 (fig. 6), there occurred, at the point where the abdominal cavities di- 

 'serged outwards, a considerable development of additional hollows, 

 which assumed immediately the nature of a new axis, but less in dia- 

 meter than that of the parent stem. How far the diverging cavities 

 entered into the composition of the off-set was not visible ; but it is 

 presumed, from the dichotomous specimen, that they contributed, for 

 a limited extent, to its composition : and a similar inference it is con- 

 ceived may be drawn respecting the instances of irregular off-shoots 

 generally. The branches gradually increased in thickness downwards ; 



