Notices of Memoirs — De 8aporta — Jurassic Plants. 277 



doubt true Floridece, with: stiff cartilaginous fronds like those of 

 Chondrus, Gelidkcm, Gigartina, etc. Their development reaches its 

 height in the Jurassic period ; but, far from being limited to that 

 period, they extend into the Chalk, and appear anew in the Flyscb, 

 towards the middle of the Tertiary epoch. The forms under which, 

 they then show themselves are so similar to those which they had 

 in the Jura, that there necessarily exists much confusion between 

 the species of the two ages, which is difficult to unravel, but which 

 witnesses at least to the persistence of the genus during a prodigious 

 space of time. The origin of the Chondrites, certainly previous to 

 the Jurassic period, is connected with the very origin of organic life, 

 since it seems more than probable that one part at least of the 

 Silurian Bythotrephis of J. Hall, and especially B. gracilis, with, its 

 varieties, differ in no respect from true Chondrites. 



Siphonites Herberfi, nov. sp., an Alga, with a simple cylindrical and 

 fistulous frond, closed at the top like the finger of a glove, more or 

 less allied to Codium, and therefore to Caulerpites, has been found 

 by M. Herbert at the very base of the Lower Lias ; it has an in- 

 contestable affinity, approaching to identity, with the Palceophycus 

 virgatus, J. Hall, a Silurian species which comes from the same 

 American beds as the Bythotrephis. 



Cancellophycus, so widely spread over the bosom of the Jurassic 

 seas, and of which' Chondrites scoparius, Thioll., is the type, is allied, 

 like Chondrites and Siphonites, though in a less direct manner, to 

 Palaeozoic genera, particularly to Spirophyton, Hall, of the American 

 Devonian, to- the Alectorurus, Schimp., of the Swedish Silurian, 

 and above all to the Caulerpites marginaius, Lesq. [Physophycus, 

 Schimp.), of the Carboniferous of Pennsylvania. The fronds of 

 Cancellophycus were fixed by the centre or the base, and formed 

 a foliaceous ex:pansion, more or less scalloped or lobed at the 

 margin, with rows of perforations disposed in ramified lines radiat- 

 ing from the point of attachment, spirally twisted, or rather 

 folded back on themselves from the periphery. The substance 

 of these fronds, probably of a cartilaginous nature, was thus per- 

 forated with a multitude of narrow and regular openings, as if 

 made by a punch. This type, which in one direction mounts to the 

 Silurian, shows itself in an opposite direction in the midst of the 

 Flyschian sea. Amongst the existing Algae, the most analagous is 

 Thalassophyllum clathrus, Post, and Rupr., a species of the family of 

 Agari, and of the order of Laminarics, which inhabits the coast of 

 Kamtchatka, and the fronds of which, pierced with regular perfor- 

 ations larger than those of the fossil fronds, attain a diameter of six 

 feet. It is probable from this resemblance that the Cancellophycas, 

 like the Agari, have formed part of the group of Laminarics, or at 

 least of a group allied to it. 



The AlgcB of the Secondary seas comprised then, according to all 

 appearance. Zoospores and Florides. The presence of Dictyotacere at 

 the same epoch is proved by the Fucoides erectus, Bean (T. Leckenby. 

 Oolitic Plants, Quart. Joum. Greol. Soc, vol. xx,, p. 81, tab. xi., figs. 

 3a and Sh), a species from the Great Oolite of Scarborough, in 



