iSSy-SS.] Remarks on the Genus Anlacodiscus Ehrb. 187 



indicate a lower position in the scale tlian delicate ones — for 

 example, compare A. gracilis, A. polygoniis, and A. scaber, with 

 A. cinctus, A. concinnus, A. mammosus ; whilst the polygonal 

 outline of A. polygonus is an advance upon the simple circular 

 of A. umbonatus, A. lucidus, A. aucklandicus, and the majority 

 of other species. It is important to point out that within a 

 single species extensive modifications may occur : the j^rimary 

 rays may be absent or well developed, or a single ray may 

 have divided and be replaced by two now contiguous and nor- 

 mally straight or regularly curved rays, as in A. Kittoni ; the 

 circular form may be replaced by the lobate, as in A. Petersii ; 

 surface depressions typical of a species may be wanting from 

 the areas where their presence would naturally be looked for, 

 as in A. excavatus. A central clear area may become excen- 

 tric, with an association of modifications dependent directly on 

 this variation, or geminate valves may be met with, but I have 

 seen none having a triple arrangement of its central spaces or 

 primary rays : this genus seems not to yield trij)lets, though 

 twin forms are not uncommon among recent West African 

 specimens of A. Kittoni var. africana, and in recent Pisaguan 

 or Vera Cruz gatherings. 



The known sj)ecies range themselves naturally into the 

 following sections: (1) Complanati, embracing A. suspectus, 

 A. Beeverise, A. simplex, A. probabilis, A, parvulus, A. Browneii, 

 A. Comberi, A. hyalinus, and A. minutus ; (2) Teneerimi — A. 

 exiguus, A. barbadensis; (3) Eadiati — A. kilkellyanus, A. 

 decorus, A. spectabilis, A. quadrans, A. dispersus, A. angulatus, 

 A. rotulus, A. grevilleanus ; (4) Areolati — A. apedicellatus, 

 A. cellulosus, A. elegans, A. radiosus, A. crux, A. margaritaceus, 

 A. scaber, A. secedens, A. compactus, A. patens ; (5) Septati — 

 A. septus, A. Schmidtii ; (6) Mirabiles — A. archangelskianus, 

 A. superbus, A. attenuatus, A. anthoides ; (7) Spectati — A. 

 polygonus, A. amffinus, A. oregonus, A. intumescens, A. afiinis, 

 A. pulcher, A. orientalis ; (8) Inflati — A. gracilis, A. for- 

 mosus, A. inflatus, A. mammosus, A. Janischii, A. carruthersi- 

 anus, A. aucklandicus, A. Wittii, A. cinctus, A. Petersii, A. 

 macraeanus, A. excavatus, A. acutus ; (9) Ornati — A. Hut- 

 tonii, A. Lahuseni, A. Sturtii, A. radiatus, A. pallidus ; (10) 

 Eetiformes — A. reticulatus, A. Grunowii, A. Eogersii, A. 



