R. M. Brydone — Neiv Chalk Polyzoa. 99 



Ooscia fairly abundant but very delicate, the one figured being the 

 only perfect one I have met with, small, and of the water-bottle type, 

 with a globose body, a strongly constricted neck, and a slightly 

 expanded lip; beneath them the margin of the aperture is deeply 

 cut away. 



Avicularia small, mandibular, apertures tending to be hourglass- 

 shaped, very numerous, every zooecium having normally on either 

 side of its head a slightly diverging pair, whose upper ends rest in 

 hollows in the succeeding zooeciiim ; others are scattered about 

 irregularly, and some of these develop long convex bodies and may- 

 become sub-vicarious. 



This species, while distinguishable from Somalostega vespertilio, 

 Hag., sp.,^ by the presence of ooecia and the almost rectangular lower 

 corners of the aperture, Avould be very near it but for the absence in 

 H. vespertilio of the apertural spine bases and pores of II. nitescens. 

 On making a special examination of some Trimingham specimens of 

 H. vespertilio I found to my great interest that ])ractically every 

 zooecium had faint traces of a similar arrangement of spines or pores. 

 H. vespertilio being confined to the Trimingham Chalk and H. nitescens 

 to the Weybourne Chalk, it may fairly be supposed that the former is 

 a direct descendant of the latter, but in this respect has not quite 

 completed its differentiation. 



HOMALOSTEGA ANTECEDENS, sp. nov, (PI. IV, Fig. 13.) 



This species is so closely allied to 11. nitesce?is that it is adequately 

 described by saying that it is slightly larger, more robust, and less 

 angular ; its aperture is very much larger in proportion, its small 

 avicularia smaller and its large avicularia larger and even fully 

 vicarious ; and its side walls do not tend to bulge out. 



It occurs rarely in the (restricted) zone of A. quadratus, Hants and 

 Sussex, and I have one specimen from the zone of 0. pilula (subzone 

 of abundant 0. pilula) of Sussex. 



EXPLANATION OF PLATE IV. 

 (All figures X 12 diams. unless otherwise stated.) 



Fig. 1. Cribrilina cicatricifera. Zone ot M. cor-anguimwi. Gravesend. 



2. ,, ,, Part of the same specimen. X 21 diams. 



3. ,, vulnerata. Trimingham. With ooecium. 

 4. 



5. Mollia laminaria. Trimingham. 



6. ,, ,, Part of same specimen. X 21 diams. 



7. ,, ,, Trimingham. Another specimen. 



8. Ilomalostega margintda. Zone of M. cor-testudinaritim. Dover. 



9. ,, ,, ,, ,, Seaford. 



10. ,, nitescens. Weybourne. 



11. ,, ,, ,, Another specimen, showing an 



operculum preserved. 



12. ,, ,, ,, Another specimen with ooecium. 



13. ,, antecedens. Zone of A. quadrattis. Sbawford, Hants. 



' Marsson, Die Bryo. d. Weiss. Schreibkreide der Inseln Eugen, p. 94, 

 taf. ix, fig. 15. 



