ALG.E. 1495 



cylindrical calcareous stems, which readily separate into their compo- 

 nent segments. Each segment is hollow, with smooth or radiately- 

 striate articulating surfaces at its ends ; the inner and outer walls 

 being porous, and the space between these being vacant. The 

 detached segments of Uteria occur commonly in the Eocene deposits 

 of the Paris basin. 



Class V. FloridevE. — This class includes a large number of 

 marine and a few freshwater Algce, which are in general red or 

 violet in colour. The thallus is very variable in form, and is often 

 much branched. Reproduction may be sexual or non-sexual. In 

 the former case fertilisation is effected by means of non-motile 

 antherozooids, the result being the conversion of the female organ 

 into a receptacle, or " cystocarp," within which spores are formed. 

 Non-sexual reproduction is effected by means of special cells 

 ("tetraspores") developed in parts of the thallus. 



With regard to their distribution in time, a few types of the ordi- 

 nary Red Sea-weeds (Delesse?'ia, Sphcerococcites, &c.) have been re- 

 cognised as occurring in the older Tertiary deposits. With these 

 limited exceptions, all the fossil # forms of this class belong to the 

 Corallines and Nullipores (Corallines), in which the thallus is hard- 

 ened by the deposition of carbonate of lime. The principal genera 

 of the family of the Corallines are Corallina, Melobesia, and Litho- 

 thamnion. 



In Corallina, the thallus is erect and branched, and is composed 

 of rounded or wedge-shaped calcareous segments, which readily 

 separate from one another. The fructification consists of " cysto- 

 carps," which are immersed and have an aperture at their summit. 

 The " Corallines " are exceedingly abundant in existing seas, but 

 little is certainly known of their occurrence in the fossil condition. 

 They are, however, stated to occur in the Eocene beds of the Paris 

 basin. 



In Melobesia the calcareous thallus is crust-like and foliaceous, 

 and is attached by the whole of its lower surface to foreign bodies. 

 The superficial layer of the stony crust is composed of minute 

 cubical cells, but the deeper cells are elongated. The "cystocarps" 

 are immersed within the thallus, and project above the surface as 

 wart-like tubercles. Melobesia has not been clearly recognised in 

 the fossil state, though it is not improbable that it will ultimately be 

 found to occur even in the Palaeozoic rocks. 



In connection with Melobesia a few words may be said about the 

 curious little calcareous bodies known as " coccoliths," since it has been 

 suggested by Carter that these are connected with the reproduction of 

 Algae belonging to this genus. Coccoliths are excessively minute cal- 

 careous bodies, of a discoidal form, which are found in the mud of the 

 deep sea at the present day, often in great numbers. Similar bodies 



vol. II. 2 Q 



