934 Prof. P. M. Duncan and Mr. W. P. Sladen on the 
XXVII.—A Note upon the Anatomy of the Perignathic Girdle 
of Discoidea cylindrica, Lmk., sp., and of a Species of 
Echinoconus. By Prof. P. Martin Duncan, M.B., 
F.R.S., &c., and W. Percy SLapDEN, Sec.L.8., F.G.S. 
A PAPER upon the anatomy of the perignathic girdle of Dzs- 
coidea cylindrica, Lmk., sp., was communicated to the 
Linnean Society, and was published in the ‘ Journal’ of that 
Society for October 1886, vol. xx. p. 48. 
It was explained (p. 56) that the perignathic girdle is 
remarkable and unique in shape, being low and surrounding 
the peristomial opening in the form of a raised, oblique, 
broad, ridge-like rmg. ‘The broad upper surface of the girdle 
is free and consists of flat or irregular slanting surfaces, the 
slant being towards the peristome and ending all round and 
outwards in a continuous and wavy free edge. This edge 
has the parts which correspond to the ambulacra thin, barely 
projecting, and reenteringly curved. ‘The parts of the girdle 
which correspond to the interradia are boldly curved out- 
wards and are large. The outer wavy edge of the girdle 
overhangs the inner surface of the base of the test. 
No sutural lines exist in the specimen (no. 40341) in the 
British Museum from which the description was taken (see 
fig. 8, p. 56), upon the interradial expansion of the perignathic 
girdle. On the other hand, the median sutures of the ambu- 
lacral parts are distinct. It was remarked, ‘ but it is not 
satisfactorily shown that there are not sutures between the 
ambulacral and interradial portions along the line of the slight 
groovings which are on either side of an ambulacrum high up 
in the peristome and at the lower edge of the inner surface of 
the girdle—that is to say, in the usual position of sutures in 
relation with branchial grooves or cuts.” 
Mention was made of the pairs of pores which are on either 
side of the median and more or less vertical suture of an ambu- 
lacrum. In ambulacrum 111. there are two pairs of pores on 
one side of the median line and a single pair on the other ; 
and in the other ambulacra, although the pores are not all 
distinctly shown, they appear to conform to the peristomial 
arrangement found in other regular Echinoidea. 
All these pores are separated from the median sutures and 
also from the ill-defined sutures between the ambulacral and 
interradial portions of the girdle. 
In September 1888 one of us received a letter from our 
friend Prof. Sven Lovén, drawing attention toa paper of his, 
read Dec, 14, 1887, and published in 1888, “On a Recent 
