180 Geological Society. 



rilOCEEDINGS OF LEARNED SOCIETIES. 

 GEOLOGICAL SOCIETY. 



June 5tb, 1918.— Mr. G. \V. Lamplugh, F.R.S., 

 President, in the Chair. 



The following communication was read : — 



' The Kelestominse, a Sub-Family of Cretaceous Cribrimoi*ph 

 Polyzoa.' By William Dickson Lang, M.A., F.G.S. 



The Kelestominaj are a sub-family of Pelmatoporidae. The 

 latter are a famil}^ of Cretaceous cribrimorph Polj'zoa, whose costte 

 are prolonged upwards as hollow spines from the median area of 

 fusion of the intraterminal front- wall. The broken ends of these 

 spines form a row of pelmata (or, if small, pelmatidia) on the 

 intra tenninal front- wall. 



The Kelestomina3 are Pelmatoporidae with an apertural bar each 

 half of which is bifid ; and the proximal and distal forks of each 

 half are fused with the corresponding forks of the other half. 

 The fused distal forks are also fused with the proximal pair of 

 apertural spines, Avhich are greatly enlarged. 



The simplest known form of this arrangement is seen in the 

 genus Kelestoma Marsson. Kelestoma is characterized among the 

 Kelestomina3 by its great oecial length, and by the great number 

 of costal. Kelestoma has the following three species, which form 

 a single lineage: — (1) Kelestoyna elongatum Marsson, with an 

 incrusting asty ; (2) a new species, Avith a bilaminar, erect asty ; 

 (3) K. scalare Lang, Avith an erect, cylmdi'ical asty. There is, in 

 this series, a slight catagenetic decrease in the number of costse, 

 and the avicularian aperture becomes somewhat more pointed. The 

 genus occm's in the Senonian, zone of Belemnitella mucronata, in 

 the island of lliigen. 



Morphasmopora, unlike Kelestoma, retains a small number of 

 costte and a short oecium ; but the thickness of the proximal 

 apertural spines, which are hardly recognizable as such, is enormously 

 increased ; the thickness of the bifid apertural bar is also increased. 

 In Morphasmopora hrydonei Lang, there are four circum-apertural 

 avicularia ; and the ])roximal apertural spines and the apertural bar, 

 though enormously developed, are not so large as in M.jukes-hrownei 

 (Brydone). The latter species has fewer costaj than the former, 

 and' but one pair of circum-apertural avicularia. There are also 

 differences in the interoecial and interstitial secondary tissue of 

 the two species. M. brydonei occurs in the island of Riigen and 

 M. jukes-brownei at Trimingham; both from the Senonian, zone 

 of Belemnitella mucronata. 



