CALAMOCRINUS DIOMED.-E. 37 



Interradial plates, the jneccs accessoircs of D'Orbigny,* have been figured 

 and desci'ibed by hiui in Guettardicriniis dihitatus (Plate I. Figs. 2, 3). 

 There are two such jDlates uniting the second and third radials laterally, 

 and separated by the first and second brachials of adjoining arms from a 

 small third interradial plate. 



In Apiocrinus Roissyanus, D'Orb., the interradials are not disconnected, 

 but form an irregular pavement of stout plates, gradually becoming smaller 

 towards the perisome (see D'Orb., Plate III. Figs. 2, 7, 8, Plate IV. Fig. I). 

 The plate in the angle of the ventral edges of the adjoining first radials 

 which connects the second radials laterally is larger than the others; it is 

 followed by a row of two plates, then three, then five ; how many there 

 are beyond is not clear from D'Orbigny's figure. 



In Apiocrinus Parkiusoni, D'Orbigny figures a small interradial in 

 the angle between adjoining axillaries (Plate V. Fig. 2). In Apiocrinus 

 Murchisonianus (D'Orb., Plate VI. Figs. 1, 2, 5) he figures two in- 

 terradial plates, the lowest of which is in the angle of adjoining first 

 radials. 



The great thickness of the pieces composing the calyx is a marked fea- 

 ture of Apiocrinus and the older fossil Apiocrinidte. The interradial pieces 

 are equally solid, as is well shown in the ring of the second radials of 

 Apiocrinus Roissyanus figured by D'Orbigny in his Plate III. Fig. 7. Be- 

 tween the second i-adials the interradials are fitted with all the solidity of 

 any of the calyx pieces proper. These lower interradial pieces, both in 

 this species and in Guettardicrinus dilatatus, are as much a part of the 

 calyx as the first and second radials themselves, with which they are con- 

 nected by the same kind of suture which unites the pieces of the calyx 

 proper (see also Figure 6 of Plate III. of the same Memoir). 



De Loriol has figured two interradial plates in Apiocrinus Meriani (Mon. 

 des Crinoides de la Suisse, Plate II. Fig. 1, and Plate III. Fig. 2, Mem. de 

 la Soc. Paleont. Suisse, IV.) ; they separate the second radials and rest upon 

 the first radials ; the radials are bevelled to receive them also (Pal. Fran?., 

 XL, Plate 39, Fig. 1, P; Plate 40, Fig. ]). 



The figures given by de Loriol of Guettardicrinus dilatatus t (Pal. Fran?., 

 XL, Plates 22, 23) show a somewhat different arrangement of the inter- 



* Hist. Nat. des Crinoides. 



t De Loriol says also that Guettardicrinus dilatatus is the only species of the genus characterized by 

 radials of the second order, forming a part of the walls of the cavity of the calyx, with numerous 

 interradial pieces not mentioned by D'Orbigny. 



