W. D. Lang — Key to some Cretaceous Polyzoa. 463 



tabular arrangement of forms nor easy means whereby the different 

 species of a genus may be compared for identification by a collector. 



Fourteen species of Entalophora are described in the Catalogue as 

 being represented in the Museum collection, and references with 

 a few words of description are given of thirty-three more described 

 forms. Without access to the works mentioned the task of 

 identification becomes impossible, and the collector can hardly be 

 blamed if he leaves alone the Cretaceous forms of Entalophora. 



It is hoped that, prefaced with a few explanatory remarks, the key 

 here given will be found intelligible. 



First, all references and descriptions without figures have been 

 ignored, because in the case of such small differences of detail as 

 occur between the ' species ' in this genus, descriptions unaccom- 

 panied by figures are useless unless (and in no case is this so) they 

 are such as to compare with the whole series of described forms. 



Next, the question of synonymy has been left alone. All the 

 figures which can be referred to this genus are mentioned, and 

 references given as in the British Museum Catalogue. In many 

 cases several figures fall under one heading: and it will be generally 

 found that they are grouped as one species in the British Museum 

 Catalogue. But by no means does it follow that the converse is 

 true ; for forms widely separated on the table may be different 

 topomorphs ^ of one species. This only demonstrates the artificiality 

 of the grouping in the key. For this artificiality no apology is 

 tendered ; for the ' genus ' itself is probably as artificial as other 

 Polyzoan genera; and the key is only meant to help the identification 

 of figured forms, and not to show genetic relationships. It is to be 

 hoped that further investigation of forms, especially with regard to 

 the horizons at which they occur, will throw light on these. Mean- 

 while the accurate recognition of described forms is the first step 

 towards their further elucidation. 



The terms used in the key are for the most part self-explanatory. 

 The size and arrangement of the apertures are the characters chiefly 

 used. The distances between the apertures are described in terms 

 of the diameter of the aperture — the vertical distance being that in 

 a proximal-distal direction — along the branch, and the transverse 

 distance at right angles to this. 



The term emergent is used of zooecia whose upper surface is 

 arched well above the general level of the zoarium, which therefore 

 has a surface with a crenulate outline. On the other hand a zoarium 

 is composed of immersed zooecia whose surface is flat, though the 

 outlines of the zooecia may be apparent thereon. The terms are 

 comparative, that is, degrees of emergence and immersion are 

 exhibited. 



The measurements and statements in the table are approximate, 

 for allowance has to be made for some zooecial variation within 

 even small pieces of a zoarium. 



1 A topomorpli is a term, applicable to Polyzoa and colonial Madreporaria, denoting 

 an individual or group of individuals differing in form from those surrounding it. 

 See Geol. Mag., 1906, pp. 66-68. 



