82 CALAMOCKIXUS DIOMED.E. 



of light on the affinities of the Echinozoa ; for the Ophiurans are in some 

 ways the most crinoidal of the Echinozoa, and yet their affinities with the 

 Starfishes on the one side and the Sea-urchins on the other are often 

 striking. 



When we examine the anal system in types in which it is disconnected 

 from the apical system,* we find that the plates of the anal system of 

 Discoidea are already quite spatangoidal in their arrangement. Cotteau 

 figures those of three species of the genus ; one in Echinides fossiles de 

 I'Algerie (Plate XII. Fig. 2, p. 165, Cotteau, Peron et Gauthier, 5°"= Fasci- 

 cule, 1879); another in the Paleontologie Fran^aise (Vol. VII. Plate 1012, 

 Fig. 6). 



Cotteau has also figured the anal system of Discoidea cylindrica, (I copy 

 here, Plate XXXII. Fig. 3, from the Rev. et Mag. de Zocil, 1876, Plate I. 

 Fig. 1,) in which the arrangement of the single ring of large plates 

 enclosing a few sm.aller plates is quite complete. 



Even in some of the Spatangoids, although the anal system is already 

 disconnected from the genital ring, we can still trace the first outer anal 

 ring made up of eleven plates, and in some cases of a second inner ring of 

 plates. See, for instance, the plating of the anal system of Pala^obrissus 

 Hilgardi (Plate XXXII. Fig. 9), and that of a large number of Spatangoids, 

 in which the plating is as regular as in any Cidarid, or that of Urechinus 

 naresianus (Fig. 10) and of Cystechinus Wyvillii (Fig. 12). 



In those Clypeastroids and Echinolamps (Plate XXXII. Fig. 6) in whicli 

 the anal system has a small number of j^lates (not more than three or 

 four), they may have taken their development as we have it in Echina- 

 rachnius parma, where, in very young specimens, the anal system has at 

 first only one plate (Fig. 1), and later other plates are developed on each 

 side of it (Fig. 2). A similar mode of development probably occurs also 

 in Echinoneus (Fig. 4). 



The same seems to be the case in the development of the plates of 

 the anal system of Hemiaster (Plate XXXII. Fig. 11). In Echinocardium 

 (Fig. 13) the central part of the anal system is covered by five plates, 



* If Cystocidaris, Zitt. (Eohinocystites, Thorns., non Hall) is really a Sea-urchin, we have the 

 anal opening (V) placed, not in the apical system, but eccentrically (interradially), and closed with a 

 pyramid of small plates, so that we might, as has been suggested by Neuraayer, look upon the interia- 

 dial position of the anal system in the regular Echini as an ancient character (Neumayer, Stamme d. 

 Thierreichs, p. 330), which has appeared again after a long period of time with the Pygasteridfe in 

 the Jura. 



