DESCRIPTIONS OF THE SPECIES. 299 



spines articulated to them (PI. XX. figs. 5, 12). When Astrocrinus i> compared 

 with any of the regular Blastoids, the normal ambulacra arc seen to lie in deep 

 depressions between the projecting lobes or interradii in such a manner that the 



lines of union of contiguous radial limbs are placed on convexities (PI. XX. figs. I. 

 12, 13, 16). On the other hand, in the regular Blastoidea, any lobedike extensions 

 of the general periphery are caused by the projection of those parts of the radial 

 plates into which the distal ends of the ambulacra are received, whereb) the inter- 

 radial sutures are placed in depressions, or, at all events, not on projecting portions 

 of the calyx {VI IV. tigs. 8, 10, 12; PI. XV. iig. 11). The azygos raj of Astro- 

 crinus, however, differs from the other four ambulacra in occupying a projection and 

 not a depression of the calyx, so that three of its four lobes are interradial, while the 

 fifth is radial (PI. XIX. fig. 1; PI. XX. figs. 1, 7-10). Although Astrocrinus has 

 been considered to be a Cystid, we have little doubt that it is a Blastoid, and closely 

 allied to the singular genus Eleut/terocrinus, as we have already explained. 



The deltoids are much larger in Astrocrinus than in Eleuiherocrinus, and as in the 

 latter type (PL XIX. fig. G) those on either side of the azygos ambulacrum differ 

 from the other three in outline (PI. XX. figs. 2, 11, 12, 15, lb). As in some species 

 of Schizoblastus (e.g. S. Sayi), the proximal ends of the deltoid plates immediately 

 surrounding the mouth are sometimes much constricted, so that one of the writers 

 was formerly misled into considering them as separate elements of the calyx. We 

 are only partially acquainted with the hydrospires of Astrocrinus, but, judging from 

 the internal appearance presented by some isolated radial plates (PI. XX. figs. 4, 18, 

 20), we think it not only possible but probable that the hydrospires were situated 

 partially or entirely within the substance of these plates, as they are in Triccelocrinus 

 (PI. XVIII. fig. 11). 



While closely related to Elcuthcrocrinus in general structure, so far as it can be 

 made out, Astrocrinus presents several points of difference from that type. It is 

 much smaller and altogether dissimilar in appearance, being flattened and more or 

 less distinctly stellate or lobate (PI. XX.). The outline varies considerably, the 

 anterior lobe (/. e . that opposite the azygos ambulacrum) being considerably produced 

 in some forms (PI. XIX. fig. 1 ; PL XX. figs. 9-13), and in others comparatively 

 short (PL XX. figs. 7, 8, 14). The four normal ambulacra cross one another nearly 

 at right angles. This is very far from being the case in Eleutherocrinus, where they 

 occupy a little more than ISO of the summit, as is well shown in our figure (PL XVIII. 

 fig. 6), so that the odd ambulacrum takes up a relatively larger portion of the summit 

 than in Astrocrinus (PL XVIII. fig. 1). Pictet's views' as to the analogy of Astro- 

 crinus with Codaster are altogether untenable. He appears to have quite forgotten 

 the hydrospires of Codaster, though they had been described and well figured by 

 Koemer. The only possible resemblance between the two types is that the summit 

 1 Traite de Talcontologie, torn. iv. p. 295. 



