iS6 Remarks on the Genus Aniacodisais Ehrb. [Sess. 



and thus it comes about that the species merge insensibly 

 into one another, through forms to which we may sometimes, 

 for convenience of reference, affix a varietal name (or the name 

 of a forma), and which may be associated with one or other of 

 two allied species, according to the " taste " of the observer, 

 without violating any law of natural relationship. The same 

 is applicable, too, to the case of allied genera. Such forms as 

 simple discs, devoid of primary rays or processes, to which we 

 give the name Coscinodiscus, seem at first sight far removed 

 from these Aulacodisci, but in the latter processes are sometimes 

 wanting, and so too are primary rays and inflated areas, whilst 

 the former may have a central area without markings (or, like 

 some Aulacodisci, a central rosette), and even submarginal pro- 

 cesses of considerable size, as in specimens of the so-called Eu- 

 podiscus jonesianus, which is associable with Coscinodiscus 

 concinnus W. Sm. as var. jonesiana, and in Coscinodiscus 

 doljeusis, C. odontophorus, C. odontodiscus, C. Eothii, and speci- 

 mens belonging to the Cestodiscoid section of Coscinodiscus — 

 that is to say, to the old genus Cestodiscus. Similarly, no 

 sharp boundary lines can be drawn between forms associated 

 with the genus Auliscus and those that now rank among the 

 Glyphodisci, Pseudaulisci, or even Eupodisci ; and so for other 

 genera. 



In the construction of the Table, the guiding principle is 

 that of transition from the simple to the more complex. Thus 

 a flat or almost flat disc, such as Aulacodiscus suspectus, A. 

 exiguus, A. apedicellatus, occupies a lower position in the scale 

 than others provided with inflations like A. Petersii, A. car- 

 ruthersianus, A. Janischii, or with elevated ridge-bearing zones 

 like A. Lahuseni, or with coarse or delicate reticula like A. 

 Argus, A. Thumii, and A. Grunowii ; specimens without distinct 

 primary rays are less evolved than others in which these are 

 sharply defined — contrast in this respect A. suspectus, A. 

 Beeverise,with A. quadrans, A. margaritaceus, or A. sollittianus ; 

 valves with processes are higher than others devoid of these — 

 for example, A. formosus, A. spectabilis, A. orientalis, as 

 against A. suspectus, A. apedicellatus (in which they are 

 absent), or A. exiguus, A. barbadensis, A. cellulosus, A. septus, 

 A. probabilis (in which they are small) ; large coarse markings 



