500 W. D. Lang — Cretaceous Cheilostome Polyzoa. 



Diagnosis. Rhammatopora in "which the angle of branching is 

 more than 45° ; the zocecia are blunt distally and taper proximally ; 

 the capitulum is bounded proximally by well-curved lines ; extra- 

 terminal front wall comparatively wide laterally ; rhamma feebly 

 developed, often not visible ; aperture ovate to elliptical. 



Type-specimen. British Museum specimen D. 22987. 



Distribution. Cenomanian, Chalk Marl ; N.E. of Cambridge. 

 F. Mockler Coll. 



Remarks. The feeble development of the rhamma suggests that 

 this structure disappears during evolution and thus Rhammatopora 

 gives rise to Allantopora. 



II. Chaeixa, 1 new genus. 



In Rhammatopora the angle of branching generally is wide, and 

 the caudal portions of the zocecia, though shorter at the beginnings 

 of each branch (each branch recapitulates a former short-caudal 

 condition), quickly resume their normal length. The resulting 

 zoarium is thus always uniserial both in design and in fact. A form 

 possessing a rhamma and generally resembling Rhammatopora has 

 been found in the Albian at Charmouth, Dorset ; but the branching 

 is peculiar, and, though strictly bilateral, does not on the whole 

 produce a uniserial zoarium. The caudse are never very long, and 

 practically absent at branching ; moreover the angle of branching is 

 small, as in Rhammatopora johnstoniana (Mantell), and the new 

 branches freely branch again on the bilateral method. The zoaria, 

 therefore, though uniserial in principle, often contain patches which 

 are actually multiserial. Two other characters of this genus are the 

 rapid increase in size, so that the daughter zooecia are often much 

 larger than their parents ; and the habit (shared with other uniserial 

 Cretaceous Cheilostomes, but very marked in this form) of eroding 

 the shell it incrusts. In the type-specimen a form of rejuvenescence 

 occurs. In the case of two large zocecia in a multiserial patch, the 

 terminal buds are small zocecia with fairly long caudse and a rather 

 wide angle of branching. The long caudse are in keeping with 

 a continuation of the branch ; but the sudden smallness of size of the 

 zocecia and widening of the angle of divergence of the branch are 

 a recapitulation of (presumably) earlier conditions in characters in 

 which the lateral branches (which normally recapitulate a short 

 caudal stage) do not recapitulate. The resulting appearance is of 

 new zoaria starting from points on an old zoarium ; so it is described 

 here as a rejuvenescence. Charixa has been found incrusting BToplites 

 splendens (James Sowerby) in the Albian, zone of Hoplites interruptus, 

 and on Gervillia forbesiana, d'Orbigny, and Exogyra conica (James 

 Sowerby) in the Albian, zone of Mortoniceras rostratum, Cowstone 

 horizon, at Black Ven, Charmouth. Also in the Gault of Dunton 

 Green, N. of Sevenoaks, Kent (B.M. specimens D. 23021-4 and 

 a specimen kindly lent me by Mr. A. G. Davis, Hon. Curator of the 

 Croydon Natural History and Scientific Society). 



1 Garixa, an old name of Charmouth (the type locality ; see Boberts, 1823, 

 "The history of Lyme Eegis, Dorset," p. 220), probably = 'Char, isca' 

 (altered to l ixa' as in Exe, Axe, &c), i.e. "Char river". I have therefore 

 altered the spelling to Charixa that this generic name may better recall the 

 locality. 



