INVERTEBRATES. 189 



This is another type, agreeing exactly with Actinocrinus in 

 the number and arrangement of the pieces composing all that 

 part of the body below the divisions of the rays. Above this, 

 however, in the structure of the succeeding parts, to the bases 

 of the free arms, it is remarkably different. After the first 

 division of the rays, another bifurcation takes place on the 

 secondary radials, and of the latter divisions the two outer 

 usually consist of a succession of brachial pieces, while the two 

 inner divisions continue on for some distance, sending off on 

 each side alternating lateral division or ranges of brachial 

 pieces, so as to produce a great number of arms. The spaces 

 between all the divisions, out to the bases of the free arms, are 

 occupied by small intermediate pieces, which, together with 

 the brachial and other divisions, unite and spread out horizon- 

 tally or at right angles to the axis of the body, so as to form an 

 enormously expanded rim around the summit (see cuts No. 5 and 

 7), which isolates the anal and interradial areas from the vault, 

 and bears the small, free, ascending arms around its margin. 

 The vault is nearly fiat, composed of numerous small pieces, 

 and extends out to the farthest limits of the expanded summit, 

 so that, as seen from above or below, it presents the appearance 

 of a broad, flat, more or less distinctly ten-rayed disc. As in 

 Actinocrinus, the arms are simple, and consist each of a double 

 series of small, interlocking pieces. The body, below the ex- 

 panded summit, in the species of this group, is more or less 

 elongate-obconical, and usually somewhat truncated at the base 

 (see cut No. 7, on p. 192), so that, with its greatly expanded 

 summit and flattened vault, it presents a symmetrical, urn- 

 shaped outline. The body plates are usually more or less 

 costate, and sometimes beautifully rayed. 



Like various other groups of palaeozoic Crinoids, as the genera are now under- 

 stood, the genus Strotocrinus includes two sections, distinguished as follows : 

 Section a. — The typical species, with a small, simple, subcentral opening in the vault 



without a projecting proboscis. 

 Including the typical species, Strotocrinus perumbrosus and S. regalis= 



(Actinocrinus perumbrosus and A. regalis, Hall). 



