296 R. M, Bnjdone—Netv Chalk Pohjzoa. 



circular. The earlier forms have as a rule sharper features than the 

 later. The ooecia (Fig. 5) are very simple, very little more than 

 mere swellings. 



In the case of S. Pergensi the original figure was quite inadequate 

 and must be withdrawn. The type was unfortunately selected from 

 a horizon at which various delicate features presented by the early 

 forms had got blunted or obscured. In the early forms from the 

 lower part of the zone of A. qtiadratus the zocecia are separated by 

 definite sutures which enable a distinction to be easily drawn between 

 the not infrequent accidental swellings of the foot of a zooecium, 

 which stop short at the suture, and the rather larger swellings which 

 pass across and hide the suture and are ooecia (Fig. 9) ; the little 

 infolds of the side walls, which give a trifoliate appearance to the 

 siperture, are sharp and strong in the early form, but tend to die away 

 in the later forms, as e.g. in the larger zooecia in the figure of part of 

 the type, thongh occasional specimens and zooecia continue to develop 

 them well (e.g. Figs. 7 and 8). The avicularia in the early forms 

 prove to be of the hourglass type, with a long elliptical aperture and 

 side walls gently infolded over a considerable length, and at their 

 maximum of infold slightly overhanging the aperture, below which 

 point they return rather sharply ; a tiny blunt denticle is often found 

 ])rojecting into the aperture from the middle of its lower end; the 

 bounding sutures (slightly exaggerated in the figures) show that 

 a deep cavity is hollowed out in the lower end of the succeeding 

 zooecium in order to receive the low upper end of the avicularium. 

 In the later forms the avicularia tend to broaden and flatten out and 

 the infold of the side walls and the apertural denticle become very 

 faint or disappear. 



EXPLANATION OF PLATES. 

 Plate XIV. 



(All figures x 12 cliams. unless otherwise stated.) 

 Fig. 1. Semieschara Proteus, var. lateaperta. Zone of H. plcmns, Froxfield, 

 Hants. 



,, 2. Semieschara Proteus. Zone oi M. cor-test2idi7iarium, Sea.ioYd. 



,,3. ,, ,, ,, Privett, Hants. 



.,4. ,, ,, ,, Seaford. 



., 5. ,, ,, ,, ,, X 21. 



,,6,7. ,, ,, M. cor-anguinum, Gra,\esend. 



,, 8. Semieschara Proteus, vax. peneclausa. Zone of A. qiiadratus (sub- 

 zone of ditto), Shawford, Hants. 



Plate XV. 



(All figures x 12 diams.) 

 Fig. 1. SemieschnraWoodsi. Zone of B. witcronato, Portsdown (type-specimen). 

 ., 2, 3. 



,, 4. ,, Subzone of 0. j;iZ!i/a, West Meon, Hants. 



,, 5. ,, ,, A. quadratus, Shawford, Hants. 



,, 6. Semieschara Pergensi. Zoneof-B.7n?(cro7iato,Portsdown(type-specimen). 

 ,, 7,8. 

 ,, 9-11. ,, Subzone of £. sc?</a/?(s, var. dfjJiTSSMS, Brighton. 



