R. M. Brydone — Chalk Zone of Holaster planus. 247 



yards. Under these circumstances the finding of a single specimen 

 of E. scutatus is devoid of any serious significance, and when it figures 

 as the sole reason for making a separation, not merely in zone hut in 

 stage, between the " Bicavea bed" and the " Vectensis bed", it is 

 obviously so inadequate that it would be outweighed by the slenderest 

 grounds for uniting these beds zonally. We are naturally led to ask 

 whether there are any such grounds. 



Accurate collecting from the " Vectensis bed " can only be carried 

 on over the very limited area, probably not as much as 100 square 

 yards all told, exposed in situ, as there is no outstanding feature by 

 which fallen blocks from this bed can be certainly identified with it. 

 I have only examined it once at Culver Cliff and twice at Compton 

 Bay, but I have obtained from it besides other fossils the following 

 significant ones : — 



Holaster planus (abundant) . 

 Pentacrinus (large ossicles in abundance). 



Bourgueticrinus (joints in great abundance, many long and slender). 

 Lophidiaster ornatus (ossicles in abundance). 

 Crania Egnabergensis (several). 

 Lima Wintonensis (several). 

 Scalpellum maximum. 



Polyzoa of twelve genera, most of which are represented by more than one 

 species, including Membranipora Vectensis and Bicavea rotula. 



Every item in this list is a strong link with the zone of Holaster 

 planus and a strong distinction from the typical chalk of the zone of 

 T. lata in the Isle of Wight at any rate. They must, of course, be 

 taken quite strictly. A solitary specimen of Lima Wintonensis or 

 Crania Egnabergensis would be unexpected without being startling 

 in the typical T. lata - chalk of the Isle of Wight, but several 

 specimens of either would compel a reconstruction of our ideas about 

 that chalk. They are regular constituents of the H. planus-ioMm., 

 as also (at Compton Bay only) is Scalpellum maximum. Lophidiaster 

 ornatus, which is fairly abundant in the Albian, is also known from 

 the Chalk zones of H. subglobosus, T. lata, LT. planus, and Ificraster 

 cor-testudinarium, but while it is abundant and very widespread in 

 the zone of H. planus it is quite scarce in the other zones. Ossicles 

 of Pentacrinus (to use the familiar name for convenience, not in 

 ignorance of Dr. Bather's correction) are not of course per se peculiar 

 to the zone of LT. planus. I have them from every zone of the White 

 Chalk, but the zone of LT. planus is the only one beside that of 

 B. mucronata in which they are not both scarce and small. Those 

 of the " Vectensis bed" are as abundant as those of the LT. planus- 

 chalk and range freely up to f in. in diameter. Ossicles of 

 Bourgueticrinus are not unknown in the typical T. lata-ch&lk. of the 

 Isle of Wight, but my experience is that they are scarce throughout 

 and always short and stout in the upper part ; in the lower part they 

 may be long, but are never slender ; those of the LL. planus-zone 

 agree absolutely with those of the " Vectensis bed ". Holaster planus 

 might occur in the typical T. lata- chalk of the Isle of Wight, but it 

 would take a long time to find a second specimen, and an abundance 

 of it is hardly imaginable. Finally, Polyzoa, numerous both in 

 species and individuals, forbid any association of the " Vectensis bed" 



