TRANSACTIONS OF SECTION C. 821 
The pebbles of the Keuper sandstone occur almost entirely about the base of 
the formation, but they are few in number and variety compared with those in the 
Bunter. They consist of vein-quartz and quartzite of various shades of light and 
dark-grey. They do not seem to have been derived from the Bunter, and it is not 
likely that it was exposed to denudation when the Keuper was deposited. Probably 
the pebbles came from the same source as those in the Bunter, when the supply had 
dwindled away and was almost limited to those of light-coloured quartzite. 
5. Notes on the Morphology of the Cystidea. 
By P. Herpert Carpenter, D.Sc., F.R.S. 
In many Cystidea the plates enclosing the lower part of the body are as regularly 
arranged as in thecup of a Crinoid. Thus in Caryocrinus, which is a hexamerous 
form, the base is dicyclic. Resting on the stem are four infra-basals, two of which 
are double plates. Above and alternating with these are the six hasals, and above 
them again isa ring of eight plates, six of which alternate with the basals and repre- 
sent the radials of a Crinoid, while the other two, each resting upon a basal, are 
supplementary or interradial plates. Memicosmites is another dicyclic and hexame- 
rous form, but has three supplemental interradials. Protocrinites too seems to haye 
a dicyclic and hexamerous base. A similar interpretation may be given of many 
pentamerous genera besides the well-known Porocrinus. Thus, in Echinoencrinus 
plates 1 to 4 of Edward Forbes’s nomenclature are infra-basals, No. 3 being a double 
plate. The sub-ovarian series, Nos. 5 to 9, alternating with them, are basals, 
while Nos. 10 to 14, thecentrolaterals, Forbes, are radials. Nos. 15 to 19, alternat- 
ing with these, and called supra-ovarian by Forbes, are interradial, and are per- 
haps homologous with the deltoids of the Blastoidea. The construction of the 
calyx in Apiocystis, Callocystis, Cystoblastus, Glyptocystis, Pseudocrinus, and various 
other well-known genera, is essentially similar to this, while there are three or 
more tiers of alternating plates in Homocystis, Lichenotdes, Macrocystella, and 
Mimocystis. In some genera the mouth was protected by five oral plates, that 
on the anal side being larger than its fellows, as in the Paleocrinoids. Cyatho- 
cystis, Glyptosphera, Spheronis, and Pyrocystis had five, while Caryocrinus had 
8lx, with the posterior one subcentral, as in the Camerata. Two of Barrande’s 
figures of Pyrocystis desideratus, which are internal and external views of the 
same specimen, show the relation of these oral plates to the ‘ hydrophores palmés.’ 
These structures were not at the dorsal pole, as supposed by a recent writer in 
‘Nature,’ but they were rightly interpreted by Neumayr as the remains of sub- 
tegminal ambulacra. In those types without a genital pore the anal pyramid 
may have subserved generative functions, as in the recent starfish Hymenaster. 
The armoured forms of the Psolidee among Holothurians, with their anal pyramid 
and oral plates, present many points of resemblance to the Cystidea. Aristocystis 
seems to have had a fourth opening near the peristome, which was possibly 
nephridial, and the similar position of the third opening in Echinoencrinus suggests 
that it, too, may have been nephridial rather than genital. 
6. On the Sources of the River Aire. 
By Professor Sitvanus P. THompson, D.Sc. 
The author proposed to explore the source of the river Aire by a method involv- 
ing the use of fluorescent bodies, such as fluorescein or its soluble derivative, uranin. 
Very small quantities of this material give a visible coloration to the surface of 
the water. He had applied this substance to test whether the water of Malham 
Tarn, which sinks into the ground about half a mile after leaving the tarn, emerges 
at the reputed ‘ Aire-head’ two miles below, or at Malham Cove one mile below. 
He incidentally noticed that there is a second water-sink, not marked as such on 
the Ordnance maps. In a preliminary experiment about 12 pounds of uranin were 
thrown into the recognised water-sink ; but after a lapse of three hours nothing 
whatever had been seen at Aire-head and nothing distinctive at Malham Cove. 
