REPORT ON THE CRINOIDEA. 33 



III.— THE CALYX. 



In all the recent Crinoids, with the single exception of Tliaumatocrinus (PI. LVI. 

 figs. 1-4), the calyx proper is formed of but two series of plates, viz., the basals, which rest 

 upon the top stem-joints, and the radials, which are supported by and alternate with the 

 basals. The plates of these two series are suturally united to their fellows and to one 

 another ; and they enclose a central cavity which is sometimes large enough to contain 

 the whole visceral mass, as in Holopus (Pis. I.-IV.) and Hyocrinus (PI. VI.). In 

 other cases, however, the internal cavity of the calyx is reduced to a minimum, and it 

 lodges nothing but the chambered organ with the plexiform gland which rises from it ; 

 while the entire visceral mass is situated altogether above it, and is very easily detached 

 from it, as in many Comatulfe, so that there can hardly be said to be any cup at all. 



Intermediate conditions between these two extremes are met with in the Bouro-ueti- 

 crinidse and Pentacrinidse. In the last named family the cup which is formed by the 

 united upper surfaces of the radials is wider than in Antedon, but somewhat more 

 hollowed than in Actinometra (PL XII. figs. 1,2, 15, 16 ; PL XVIII. figs. 4, 5 ; PL XX. 

 figs. 5, 8; PL XXVI. fig. 11 ; PI. XXX. figs. 3, 4; PL XXXIII. fig. 5; PL XXXIV. 

 figs. 7, 8 ; PL L. figs. 5, 6) ; and the lowest portion of the visceral mass rests in this 

 concave upper surface of the radial pentagon ; while the greater part of it lies in the cup 

 which is formed by the outer radials and lowest distichals (PL XVII. fig. 5 ; PL L. fig. 1 ; 

 PL LXIL). But the central funnel of the calyx, which is between the inner faces of 

 the radials, only contains the plexiform gland ascending from tlie chambered organ 

 (PL LVIII. fig. 3, x). 



This is also the case in Rhizocrinus and Bathycrinus (PL Vllb. figs. 1, 4, 5, a;). In 

 the former genus the upper surface of the calyx has a deep hollow which lodges a portion 

 of the intestinal coil (PL X. figs. 1, 4, 6, 7, 8); while the upper part of the visceral 

 mass is entirely supported by the first four brachials in two syzygial pairs (PL X. 

 figs. 2, 20). In Bathycrinus, however, the gut hardly descends to the level of the first 

 radials ; and though the visceral mass is very largely supported by the large wing-like 

 processes of the axiUaries, it is practically quite free from the lowest brachials (PL VII. 

 fig. 3; PL Vllb. figs. 1, 7, 8). 



Concealed in the lower portion of the calyx is the chambered organ, the position of 

 which, relatively to the calyx-plates, varies considerably. In aU the Comatulse it is lodged 

 within the cavity of the centro-dorsal, and it is therefore entirely on the dorsal side both 

 of the radials and of the basals, whether the latter have been metamorphosed into a 

 rosette or not. But in the stalked Crinoids there is no enlargement of the central 

 canal of the stem within its uppermost joint, and the vascular axis passes up into the 

 calyx before expanding to form the chambered organ. In Rhizocrinus, Bathycrinus, and 



(ZOOL. CHALL. EXP. — PART XXXII. — 1884.) li 5 



