Anatomical Nomenclature of Echinoderms. 13 



Avhich lodged the extensor ligament (muscle?). The plates 

 of attachment for the flexor muscles between the first and 

 second radials are in a more vertical position than the rest of 

 the articular face, and when the second radials are in position 

 five clefts are visible on the floor of the calyx, which were 

 occupied during life by the five pairs of muscular bundles. 

 These clefts are particularly well shown in Zittel's own figure 

 of the interior of the cup of Apwcrtnus Parkinsoni*, while in 

 de Loriol's more recent figure of the same species f they like- 

 wise appear, together with precisely similar clefts between the 

 radial axillary and the two brachials which it bears. The 

 existence of a muscular articulation is admitted in the latter 

 case, and it will scarcely be any longer denied that there is a 

 similar articulation between the first and second radial. It is 

 a peculiar one no doubt, owing to the gTcat size of the dorsal 

 fossa in some species of Apiocrinus. But this is well deve- 

 loped in some species of Millericrinus, e. g. M. ranvillensis^ 

 and a regular gradational series may be traced from the most 

 PewtocriV? ws-like forms oi Millericvinus through M. ranvillensis 

 to Apiocrinus elegans, and thence to forms like A. Meriani 

 and others with large dorsal fossa3. 



Even in these last there are distinct indications of a mus- 

 cular articulation, while whenever the distal faces of the 

 second radials or the proximal faces of the axillaries are 

 visible they present a vertical articular ridge for a bifascial 

 articulation, exactly as in Antedon rosacea and in most 

 Comatulce J. We find therefore that in the calyx of Apio- 

 crifius there are two articular facets below that on the axil- 

 lary radial, which is the first one admitted by Zittel ; and if 

 Schnitzels nomenclature be followed, Apiocrinus must be 

 described as having but one radial, like Encrinus and Penta- 

 crinus. The same will be the case with every other Neo- 

 crinoid except Guettardicrinus, a genus which, as defined by 

 d'Orbigny, is not admitted by Zittel; but de Loriol has 

 pointed out that in this type there are no articular facets on 

 either of the three radials, nor even on the distal faces of the 

 second joints after the axillary § ; and, in fact, it has not yet 

 been determined what plate of the body of this type does bear 

 the first facet. 



If, then, Schultze's nomenclature is to be extended to the 

 Neocrinoids, Ouettardicrinus is the only type which can be 

 said to have more than one radial. 



Steinmann and Doderlein || admit that the arms sensu stricto 

 * Op. cit. p. 389, fig. 277 h. f Op. cit. pi. xxx. figs. 1 a, 1 b. 



X De Loriol, oji. cit. pi. xxx. fig. 2 b, pi. xxxiii. fig. 2 a, pi. Ivi. figs. 2, 2 c. 



§ Op. cit. p. 219. 



II ' Elemeute der Palaontologie,' Leipzig, 1888, p. 153. 



