68 W. D. Lang — T/ie Replant Eleid Polyzoa. 



show that this phenomenon of isolated patches of abnormal zooecia 

 occurs commonly among Polyzoa. And for these local forms 

 I propose the name Topomorph, a purely morphological terra, 

 describing any part of the zoarium in which the zooecia differ 

 from those of the I'est of the zoarium. Thus it includes, for 

 instance, growth stages, "localised stages,"' peculiar forms due 

 to external conditions such as overcrowding or a dififei'ent food 

 supply, to possible intermittent or seasonal causes such as repro- 

 ductive activity. The characteristic of the term is its freedom 

 from physiological implication, and herein lies its value, for it 

 can be used in morphological descriptions before the origin or use 

 of the described parts is known. Whereas the terms variety (as 

 in the case of var. plana above), stage, etc., imply systematic or 

 developmental relations which on further investigation may or 

 may not be found to hold ; and the term ' form ' (as, for instance, 

 Sparsicavea carantina, d'Orbigny, form franquana) is far too useful 

 and too widely used as a general term applicable to zooecium, 

 zoarium, or parts of a zoarium, and to members of other groups 

 of organisms, to be limited by a technical and special significance. 

 To describe a part of a zoarium of a species of Memhranipora in 

 which the apertures were ovate as a topomorph of species x, atid 

 to describe it again as a growth stage of the species, because it has 

 been discovered that a stage with circular apertures always precedes 

 and one with elliptical apertures alwaj'S succeeds it, implies no 

 incongruity nor contradiction, because the first is a morphological 

 term describing structure, and the second a physiological term 

 describing the behaviour of the species. 



It is hoped that this paper, though adding little to what is 

 already known about the Eleids, may be of some use to the 

 collector in helping him determine the species by presenting them 

 in a tabular arrangement, that the occurrence of forms new to 

 England may stimulate further collecting, and that the suggestions 

 concerning generic distinctions may place in a more hopeful light 

 the ultimate discovery of the evolution within the group and of the 

 true relations of its members among themselves. 



EXPLANATION OF FIGUEES IN TEXT. 



Figs. 1-11. — Diagrammatic representations of apertures of Eleids. 

 All the figures are very much enlarged, but their sizes are not comparative. 



Fig. 1. K'^Qviviie oi Eeptelea Ugericnsis {iX'Ovhignj). After d'Orbigny. 

 ,, 2. K\}eYi\ixe ol Iteptelea pyriformis [MicXioim). After Micheliu. 

 ,, 3. Apertui-e of i(!^'ji;ie/m «c<(«o?> (d'Orbigny). After d'Orbigny. 

 ,, 4. Aperture of Semimultelea Dixoni, n.sp. From the t}'pe-specimen (B.M. 



D7845). 

 ,, 5. Aitertnre oiBcptoeeritites Boivei, Gregory. From the tj'pe-specimen (B.M. 



D4244). 

 ,, 6. Aperture of Semimultelea irreffularis, d'Orbigny. From the specimen 



B.M. D 4867. 



1 I.e. local recapitulations. See E. T. Jackson, "Localised Stages in Develop- 

 ment" : Mem. Boston Soc. Nat. Hist., vol. v. No. 4 (1899), pp. 92, 139, 141. See 

 also W. D. Lang, " Stomatopora antiqua, Ilaime ": Geol. Mag., 1905, pp. 259,260. 



