XXXV] MALACOTESTA 363 



tudinal ribs : it is radially symmetrical and does not conform in 

 this respect to Arber's definition of Platyspermum. In many 

 cases, e.g. the flattened seed figured by Kidston as Rhabdocarpus 

 multistriatus, it is impossible to determine the symmetry of the 

 seed. The old generic name Carpolites, Carpoliihes or Carpolithus 

 has been used in a very wide sense and does not connote any well- 

 defined features; it should be reserved, in the form Carpolithus 

 as used by Linnaeus, for seeds that cannot be assigned to a system- 

 atic position or which do not exhibit any distinctive characters 

 worthy of emphasis by the institution of a special name. The 

 generic term Holcospermum, recently proposed by Nathorst 1 , is 

 a suitable name for this type of seed; as defined by the author, 

 it includes seeds that may be radiospermic or platyspermic. 

 Specimens of the type-species, Jf/. dubium 2 ,hom the Lower Carboni- 

 ferous beds of Spitzbergen, agree closely in size and shape with 

 some examples of Rhynchogonium and Boroviczia, but they are 

 distinguished by prominent ribs extending the whole length of 

 the cast. In some seeds similar to H. sulcatum the ribs form sharp 

 ridges, but the difference between rounded and sharp ridges is 

 often determined by the method of preservation: a specimen 

 deprived of its outer flesh would form a cast more sharply ribbed 

 than a seed in which the sarcotesta had been moulded on to the 

 ribbed sclero testa. On the other hand some ribs are formed by 

 blunt sclerotestal folds as in Colpospermum : both types of ribbing 

 are included in the genus Holcospermum. 



ii. Other Genera, 



Malacotesta. Williamson. 



This generic name was instituted by Williamson 3 for a petrified 

 seed from the Coal Measures of Lancashire which he named 

 Malacotesta oblonga : the type-specimen is a small seed 6 7 mm. 

 long characterised by a thick fleshy integument. The struc- 

 ture is however insufficiently known to admit of a satisfactory 

 comparison of the imperfectly preserved specimen figured by 

 Williamson with other types. 



1 Nathorst (14) p. 28. 2 Ibid. PL xv. figs. 53, 54. 



3 Williamson (77) B. p. 246, PL xm. figs. 8893. 



