IN THE MOEPHOLO&Y OF THE CTSTIDEA. 17 



appears in Augelin' s ' Iconograpliia ' * may be interpreted in tlie 

 same way, and the small peristomial plates whieb appear to belong 

 to the ambulacral skeleton are well seen in bis figures of the 

 summit t. One of the latter also shows the low pyramid of five 

 oral plates, one of which is considerably larger than its fellows. 

 The large one, however, is not that of the anal interradius (CD) 

 as in Sphceronis, but that of the next one (DE), in which the so- 

 called genital opening is placed. 



In the preceding pages I have endeavoured to show that many 

 Cystideans have a calycular system which is essentially similar to 

 that of tbe Crinoids, and I cannot, therefore, agree with Loven J 

 when he sajs: — "In the Cystoidea — in which every trace of a 

 calys is wanting, at least in the adult — the basal part of the 

 skeleton is formed by the perisome alone." This seems to me 

 to be far too general a statement, though it is no doubt applic- 

 able to SphcBroiiis , Qlyptosphcsra, and similar forms. But I can 

 scarcely imagine that Loven will deny the presence of a calyx in 

 such forms as Gystoolastus (PI. I. fig. 7), or even in Garyocrinus 

 (fig. 2), though he a.ppears to believe this to be the case in 

 Gallocystis (fig. 5). 



2. The Summit Opekings. 

 Most palaeontologists now believe that the mouth of a Cystid 

 was placed at the point of convergence of the ambulacra, as is the 

 case in all the other Echinoderms, and the anal function of the 

 lateral valvular opening has been generally acknowledged for 

 some time past, as may be seen in any standard text-book of 

 zoology and palaeontology, though Sturtz § has recently suggested 

 that it may represent the madreporic opening of Starfishes. 

 Under these circumstances it is not a little unfortunate that the 

 whole question should again have been thrown into confusion by 

 S. A. Miller, whose utterances on the subject of Cystids in his 

 recent volume on North American (xeology and Palaeontology are 

 vague in the extreme. He admits that the mouth of a Blastoid 

 was situated at the point of convergence of the ambulacra, and 

 that the lateral opening was the anus. In his diagnoses of 

 Glyptocystis and Gom'phocystis, however, he calls the latter the 



* Op. cit. tab. xii. fig. 2. t Ibid. figs. 3-5. 



j " Ou Fourtalcsia, a Genus of Echinoiclea," K. Sveusk. Vetensk. Akad. HanclL 

 1883, Ed. xix. No. 7, p. 10. 



§ " Neuer Beitrag zui- Kenntniss palajozoischer Seesterne," Palceontographica, 

 Bd. xxxvi. 1890, p. 242. 



LINN. JOUEN. — ZOOLOGY, VOL. XXIV. 2 



