THALLOPHYTES, BRYINAE. 39 



calcareous mass, which thus forms a thick hollow cylinder about the axile 

 tube. The exterior terminations of the members of the second order, which 

 cohere laterally and form a rind, are never calcified ; it may be presumed 

 that they are chiefly concerned in the work of assimilation, and they cause 

 the prettily areolate appearance of the surface. Fig. a on page 38, which is 

 drawn from nature, will serve to illustrate this description. 



Among fossil forms the genus Polytrypa, Mun. Chalm. has absolutely 

 the same structure as Cymopolia, and therefore Munier Chalmas most 

 properly unites the two genera. Polytrypa, like most of the forms which 

 we are about to consider, is found in the sands of the Eocene deposits in the 

 neighbourhood of Paris. Only the calcified parts of course are preserved, 

 and the whole plant is therefore broken up into its several members by the 

 disappearance of the portions forming the joints. Each member shows a 

 broad central canal (the main axis) with secondary verticillate systems of 

 canals proceeding from it and passing through its calcareous ring ; the 

 middle branches of the whorls end of course blindly in the cavities of the 

 sporangia, while the lateral branches, traversing the whole breadth of the 

 calcareous matter as slender canals, are open to the outside, where they 

 appear in the form of circular pores. They are thus open externally, 

 because the bladder-shaped outer extremities of the cells not being calcified 

 have one and all disappeared. 



The type of Gumbel's genus Haploporella is Carpenter's l Dactylopora 

 Eruca, a form which is said to be still living in tropical seas, and which is 

 based on the recent genus Neomeris, Harv., as I shall presently endeavour 

 to show. It is left by Munier Chalmas with Polytrypa-Cymopolia, and 

 represents the type of the section Decaisnella, which, as I have said, I am 

 unable to distinguish from Neomeris. The thallus of Neomeris is simple 

 and unbranched, and answers to a single calcified member of Cymopolia 

 which has elongated by apical growth and may ultimately attain consider- 

 able dimensions. The whorls of branches are also like those of Cymopolia, 

 but never bear more than two branches of the second order beside the 

 sporangium, and these always occupy the median position. Moreover, the 

 calcification is less copious and never results in the formation of a homo- 

 geneous cylinder inclosing all the lateral branch-systems ; it is in fact only 

 round the sporangium and round the swollen extremity of the branch of 

 the first order which bears it, that it is developed to any considerable 

 extent and that it forms a crust. Hence it is that these parts only are 

 preserved ; the slight laminae of lime which clothe the branches of the 

 second order were not firm enough to resist disintegration. The whole 

 plant therefore in the fossil state has separated into a countless number of 

 small pieces, each of which usually conceals a sporangium. A single canal, 



1 Carpenter (1). 



