66 W. D. Lang— The Rqyfant Eleid PoJyzoa. 



zooecial characters the two species SemimuUelea irregularis, d'Orbigny, 

 and Beptelea pnlcheUa, d'Orbigny, appear inseparable. This con- 

 clusion has been reached after the examination of specimens in 

 the British Museum collection referred by Gregory to these two 

 species. Nor can they be distinguished zooecially by the diagnoses 

 given in the British Museum Catalogue. It seems, tlierefore, that 

 here are two species of one genus — the more primitive possessing 

 a zoariura which, when adult, consists of an encrusting unilaminar 

 sheet of zooecia; the other, whose adult zoarium is in a more advanced 

 stage, namely, hi- or paucilaminar, passing through an immature 

 unilaminar stage corresponding with that of the adult of the more 

 primitive species. 



Beptomultelea Bowei, Gregory, and SemimuUelea Dixoni, Lang, are 

 another pair of species approximating in zooecial characters, and 

 differing chiefly from the two pi'eceding species in the size of the 

 apertures. These four species appear to be more nearly related to 

 each other than to any other reptant forms, and possibly form 

 a single genus. Similarly, the species or groups of species marked 

 A, B, C, and E possibly indicate so many difi'erent genera. But 

 before more certain conclusions can be formed the erect forms will 

 have to be considered, more specimens must be forthcoming, and 

 especially must the various stages in the life-history of the zoaria 

 of different species be examined. As the facts stand it seems 

 probable that zooecial characters rather bear generic and zoarial 

 specific significance. Such a general law, however, must not be 

 applied blindly, but always with i-egard to its bearing upon 

 evolutionary series; and the test for a common genus among several 

 species exhibiting similar zooecial chai'acters must be the identit}^ of 

 developmental stages in zoarial growth. 



IV. TOPOMORPHS.^ 



In the discussion above on generic and specific determination, two 

 characters have been disi'egai-ded — the presence or absence of 

 avicularia and of closed zooecia. 



Scattered irregularly among the normal zooecia of the reptant 

 ' genera ' Beptoceritites and Beptomultelea are individuals of extra- 

 ordinary shape, generally having the distal portions of the aperture 

 drawn out to form a long tongue. Such individuals have been 

 considered the homologues of avicularia in Cheilostomes, whose 

 function is regarded as protective. The nature of the Eleid 

 avicularia is fully discussed in the British Museum Catalogue.- What- 

 ever their physiological significance, the morphological fact remains 

 that their distribution is irregular. Never very frequent, they are 

 often so rare that large portions of the zoarium are free from them. 

 For instance, from the large zoarium of the figured specimen of 



