Vll] CODIUM. 159 



of the rock and they are not confined to the lines of bedding ; in 

 none of the examples is there any trace of carbonaceous matter 

 in association with the deep moulds. On the whole, then, this 

 Kimeridge fossil cannot, I believe, be accepted as an authentic 

 example of a Mesozoic Caulerpa. 



It is not improbable that some of the supposed fossil algae 

 may be casts of egg-cases or spawn-clusters of animals. In 

 Ellis' Natural History of the Corallines' there is a drawing 

 representing a number of disc-like ovaries attached to a tough 

 ligament, and referred to the mollusc Buccinwm, which bears a 

 certain resemblance to the Weymouth fossil. A similar body 

 is figured by Fuchs^ in an important memoir on supposed fossil 

 algae. 



It is not suggested that the Caulerpa Carruthersi of 

 Murray should be regarded as the cast of some molluscan 

 egg-case attached to a slender axis, but it is important to bear 

 in mind the possibility of matching such extremely doubtful 

 fossils with other organic bodies than the thallus of a Caulerpa. 

 In an example of an egg-case in the Cambridge Zoological 

 Museum, referred to a species of Pyrula, there is a hard, long 

 and slender axis, bearing a series of semicircular chambers divided 

 into radial compartments. The whole is hard and horny and 

 might well be preserved as a fossil. 



/3. Codiaceae. 



The members of this Order present a considerable diversity 

 of form as regards the shape of the plant-body ; the thallus of 

 some species is encrusted with carbonate of lime. The order 

 is widely distributed in tropical and temperate seas. 



Among the recent genera Penicillus and Codium may be 

 chosen as important types from the point of view of fossil 

 representatives. 



Codium. 



The thallus of Codium consists of a spongy mass of tubular 



cell-branches which are differentiated into two fairly distinct 



.regions, an outer peripheral layer in which the branches have 



1 Ellis (1755) PI. XXXIII. a p. 86. ^ Fuohs (95) PL viii. fig. 3. 



