204 BR. W. D. LANG ON [>ol. lxxiv, 



8. The Kelestomina : a Subfamily of Cretaceous CRIBRI- 

 MORPH POLYZOA. By WlLLIAM DlCKSON LANG, Sc.D., 



F.G.S. (Head June 5th, 1918.) 



1. Introduction. 



In 1908, under the name Cribrilina jiikes-brownei, Mr. Brydone * 

 described a Cretaceous cribrimorph Polyzoan of remarkable struc- 

 ture. There is little bej^ond its cribrimorph intra terminal front- 

 wall to connect it with Cribrilina ; 2 indeed, at the time of the 

 establishment of C. juhes-brownei its affinities were unknown for 

 lack of correct interpretation of certain of its more specialized 

 features ; and, were it not for the subsequent discovery of an allied 

 species, Morpheas mop or a bri/donei? connecting the highly-specia- 

 lized M. \_Cribrilina], juhes-brownei with a less-specialized form 

 from Rugen described by Marsson under the name of Kelestoma 

 elongatumf the extraordinary modifications of Movphaswopora 

 juhes-brownei might still be unexplained. 



Kelestoma and Morplutsmopora are quite separate, though 

 allied, genera of Pelmatoporidse, isolated from the rest of the 

 family and constituting the subfamhV Kelestominse. The Pel- 

 matoporidse are a very large assemblage of Cretaceous cribrimorph 

 Polyzoa, that is, of Cheilostome Polyzoa whose intraterminal 

 front- wall is built of more or less fused terminal spines. The 

 family consists of those whose fused spines (costa?) are produced 

 as hollow outgrowths upwards beyond their fusions ; the broken 

 ends of these form rows of pelmata (when of small diameter, 

 pelmatidia) on the surface of the intraterminal front-wall. The 

 complete family was dealt with in summary detail in 191 u', 5 and 

 its largest section, the subfamily Pelmatoporinae, in a more 

 expanded manner in [1919]. 6 Its various subfamilies may be 

 derived from a hypothetical ancestral Pelmatoporid, and, in order 

 to explain the structure and evolution of the Kelestominas it is 

 convenient first to examine this lrypothetical Pelmatoporid ancestor. 



II. The Primitive Pelmatoporid (fig. 1). 



To arrive at such an ancestral form it is necessary to strip from 

 the various Pelmatoporid subfamilies all that is specialized in 

 them and all that is exclusively diagnostic of them, thus discovering 



5 R. M. Brydone, Geol. Mag. dec. 5, vol. iii (1906) p. 297 & fig. 9 on p 298. 



- The inaptness of applying Recent generic names to Cretaceous Polyzoa 

 was realized by Brydone (see op. cit. p. 292). 



;i W. D. Lang, Ann. & Mag. Nat. Hist. ser. 8, vol. xviii (191G) p. 8."). 



4 Th. Marsson, ' Palasontologisehe Abhandlungen ' vol. iv (1887) p. 99. 



r> W. D. Lang, op. cit. pp. 83-112. 



f * W. D. Lang, Phil. Trans. Roy. Soc. ser. B [vol. ccix]. The paper, read 

 in November 1917, is in the press. 



