234 Prof. P. M. Duncan and Mr. W. P. Sladen oji the 



XXVII. — A Note upOTi the Anatomy/ of the PerignatMc Oirdle 

 of Discoidea cylindrica, Lrak.^ s/>., and of a Species of 

 Echinoconus. By Prof. P. Martin Duncan, M.B., 

 F.E.S., &c., and W. Percy Sladen, Sec.L.S., F.G.S. 



A PAPER upon the anatomy of the perignathic girdle of Dis- 

 coidea cylindrica^ Lnik., 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 ring. The broad upper surf ace 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 inteiTadial 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 III. 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 Loven, drawing attention to a paper of his, 

 read Dec. 14, 1887, and published in 1888, " On a Recent 



