THE PAST HISTORY OF MONOCOTYLEDONS 169 



Pandanus and some of the Cycadales is illustrated by the suggestion 

 made by Saporta that Goniolina from the Kimmeridge clay and 

 Corallian of France (probably a siphoniaceous Alga) and IVilliatn- 

 sonin (a member of the Bennettitales) should be referred to the 

 Pandanacere. 



II. Helohie/E. 



iv. ^aiadacecB. 



Some of the forms placed in Naias are not very well characterised 

 as such, but fruits resembling those of this genus have been found at 

 Qilningen. The leaves called N. stylosa and N. effiigiata by Heer 

 are doubtful, and N. striata of Spitzbergen has but one instead of 

 2-4 styles. In the Interglacial beds four species of Naias are found 

 in Britain. Now only two exist, and they are very local. Very 

 unsatisfactory are the genera JVaiadita, JVaiadopsis, Naiadonum, 

 Sphoiophora, Marimi77ia. JVaiadita lanceolata is now shown to be a 

 Lycopod, and is placed by Miss Ijerna Sollas,i in Lycopodites, after 

 being compared with Fontinalis- as a fresh-water moss. Possibly 

 Alarimima is a member of the Casuarinese. 



v. Pota?)iogetonacecB. 



Of fossil pond-weeds, etc., a goodly number must be relegated to 

 other groups or to oblivion. The living forms are in general marsh 

 or aquatic plants. The submerged and floating leaves differ so largely 

 amongst themselves within the limits of the same species, and are 

 fashioned so nearly upon the same plan in a number of families of 

 different affinity that an exact determination of fossil Potamogeto- 

 naceae or Naiadaceae is rarely to be made. 



Some fossils have been placed in Posidonia and in Cymadocea, and 

 Brongniart instituted the genus Caulinites for some forms, but the 

 latter is of such an artificial nature that it is of no value, and 

 contains widely different plants. Some of those referred to 

 Posidonia may better be placed in Zostera, e.g. P. cretacea, 

 S. and M., Westphalia, P. perforata, S. and M., Eocene, Gelinden. 

 The fossils referred to Thalassocaris, Debey, of the chalk of 

 Aix-la-Chapelle, Westphalia, Maestricht, may perhaps be placed in 

 Posidonia. There seems little doubt that plants allied to Zostera 

 existed in Cretaceous or at least early Tertiary times forming the 

 same submarine meadows that they do to-day. Some Tertiary 

 fossils have been referred to Zostera, viz. Zostera ungeri, Heer, 

 Zosterites marinus, Unger, Radoboj, etc. Zostera marina, L., is 

 found in Neolithic beds in Sweden. 



The dimorphic character of the leaves of Potamogetoji is well- 

 known, and consequently the distinction between species, if rightly 

 referred to the genus, is very unlikely to be always accurate in the 

 case of fossil genera. 



^ "Quart. Tourn. Geo). Soc.,"vo]. Ivii., 1901, pp. 307-12, pi. xiii. 

 - Gardner,"" Geol. Mag.," 1886, p. 495. 



