MONOGRAPH OF THE EXISTING CRINOIDS. 109 



or even below, the dorsal surface of the radials, and quite devoid of cirri (see figs. 

 153-159, p. 221, 162, p. 223, 164, p. 227, and 168-170, p. 229). 



(2) The Cirri are slender articulated appendages of practically uniform thick- 

 ness arising from the pits or cirrus sockets on tho sides of the centrodorsal (see 

 figs. 96-98, p. 159, 306, 307, p. 265, 308, 309, p. 267); they serve to attach the animal 

 to the sea bottom or to other organisms, such as sponges, corals, gorgonians, fuci, 

 hydroids, etc. The cirri are composed of a number of segments known as Cirrals, 

 which, within narrow limits, is definite for each species; they end in a sharp curved 

 Terminal claw (see figs. 4, p. 63, 314-318, p. 273); the last segment before this termi- 

 nal claw, known as the Penultimate segment (see figs. 314-318, p. 273), usually bears 

 dorsally at or near the distal end a more or less developed sharp process, the 

 Opposing spine (see fig. 4, p. 63), which opposes the terminal claw, the two terminal 

 segments together resembling somewhat the chela of a crab; but in the comatulid 

 the articulated digit is, on account of its very close ligamentous union with the 

 penultimate segment, immovable. 



The cirrals, more especially those in the distal part of the cirri, and more 

 especially in long cirri, often bear upon the dorsal side sharp single (see fig. 333, p. 283), 

 or double (see fig. 350, p. 291), more rarely triple (see fig. 348, p. 289), Dorsal spines 

 or tubercles (see fig. 370, p. 299), or serrate Transverse ridges (see fig. 352, p. 2!)1), 

 and are usually more or less compressed laterally. 



In cases where the proximal part of the cirrus is without dorsal spines and 

 rounded in cross section, and the distal part is laterally compressed and dorsally 

 spinous, the transition between the two parts is frequently effected within the 

 compass of a single segment, which resembles tho preceding proximally and the 

 succeeding distally, and is usually darker in color than any of the other segments; 

 such a segment is known as a Transition segment (see fig. 4, p. 63). 



(3) The Basal rays (see figs. 12, p. 65, and 229, p. 247) appear externally as 

 usually small low tubercular prominences, rounded or more or less rhombic in out- 

 line, just above the proximal margin of the centrodorsal, between the bases of 

 adjacent radials (see fig. 415, p. 319). They are frequently entirely absent, or they 

 may be present in only a few of the five interradial angles. 



(4) The Eadials (see figs. 14, p. 65, and 30, p. 71), five in number (ten in the two 

 genera Promachocrinus and Thaumatocrinus) , (see figs. 113, 114, p. 181, and 505, 

 p. 371), usually appear externally as narrow oblong or more or less crescentic plates, 

 usually somewhat concave anteriorly, and always convex exteriorly (dorsally), 

 protruding beyond the edge of the centrodorsal; but in many genera they barely 

 reach the edge of the centrodorsal, while in other genera they may be entirely 

 concealed by it. 



(5) Following the radials there are (except in two genera in which a single 

 undivided series of ossicles arises from each radial) from one (the commonest num- 

 ber) to eight or nine Division series (see figs. 61, p. 87, 116, p. 183, one, 75, p. 128, 

 two, 81, p. 134, three, 164, p. 227, four or five) of two, three, or four ossicles 

 each, each terminating in an axillary from which two similar derivative-;, 

 either further division series or undivided arms, arise. These division series, 

 usually all morphologically homologous, are known, in order of their occurrence 



