REPORT ON THE CRINOIDEA. 23 



possibility of their becoming attached to floating timber does not seem so very distant after 

 all. They may have been attached above by a slightly spreading base as on the modern 

 telegraph cables ; or, on the other hand, they may have been drifted in large numbers 

 by the currents after detaching themselves from their original base of attachment. 



Occupying the innermost part of the stem of a Pentacrinite, and lodged within its 

 central canal, is its internal vascular axis (PL XXIV. figs. 1-5 ; PI. LXIL). This 

 consists of five peripheral vessels arranged around a central one. The former 

 PL XXIV. figs. 2-5 ; PL LVIII. fig. 3 — ch') are downward extensions from the chambers 

 of the quinquelocular organ within the calyx (PL XXIV. figs. 6-8 ; PL LVIII. 

 figs. 1-3— c/i; PL LXIL) ; while the latter (PL XXIV. figs. 2-5, v.) is similarly 

 connected with the axial vessel or vessels of the chambered organ (PL XXIV. fig. 6 ; 

 PL LVIII. figs. 1-3 — V. ; PL LXIL). This central vessel does not increase in size at 

 the nodes, where the peripheral vessels expand considerably, so as to form a miniature 

 chambered organ (PL XXIV. figs. 3, 4, ch.n.) ; and each chamber gives off one cirrus- 

 vessel (fig. 4, cv.). The fibrillar sheath around the chambered organ in the calyx 

 (PL XXIV. figs. 6, 7 ; PL LVIII. fig. l—ca; PL LXIL) is continued down the stem, 

 around its vascular axis (PL XXIV. figs. 1-5, ca; PL LVIII. fig. 3; PL LXIL). 

 It is sometimes closely surrounded by a more or less complete ring of pigment masses, 

 similar to those which occur in the surrounding tissue (PL XXIV. figs. 2, 5, p.) ; but 

 in other parts of the same stem these are absent in the immediate neighbourhood of the 

 central axis (figs. 3, 4). Radiating extensions of the latter are frequently to be seen 

 (fig. 1. fig. 2, ca'). They proceed outwards into the organic basis of the skeleton, and then 

 become lost, though they probably reach the epidermis, like the similar branches from the 

 axial cords of the arms and pinnules, to which a nervous nature has long been attributed. 



B. BOURGUETICKINID.E. 



The type of stem which occurs in this family differs in many respects from that 

 characteristic of the Pentacrinidse. The joints are very variable in their relative propor- 

 tions, instead of being uniformly discoidal ; they never form syzygial unions, liut are 

 freely movable upon one another, and are connected by successive pairs of hgamentous 

 bundles instead of being strung, as it were, upon five tendons of variable length. 



In the only two recent genera which belong to this family, Bathycrinus and 

 RMzocrinus, one or more of the young upper stem-joints are simple circular disks, with 

 little or no markings of any kind upon their terminal faces (PL VII. figs. 1-3, 11 ; 

 PL Vila. fig. 3-6 ; PL Villa, fig. 1 ; PL IX. figs. 1-3 ; PL X. figs. 2, 9, 10 ; PL LIII. 

 figs. 7,8). But lower down the stem the joints become first cuboidal and then elongated, 

 so that their length may be two or three times their diameter (PL VII. figs. 1, 10; 

 PL Villa, figs. 2, 3 ; PL IX. figs, 1, 3 ; PL LIII. figs. 7, 8). The younger of these 

 elongated joints are simply cylindrical ; but the older ones are more dice-box shaped mth 



