136 THE CRINOIDEA 



the name Lobolithus, and described by Hall as a float, which he 

 called Camarocrinus. 



As regards the internal organs of the crinoid not much can be 

 said. The most remarkable modifications are those affecting the 

 Gut. In most recent crinoids this makes a simple dextral coil 

 around the thecal cavity, from central mouth to eccentric anus. 

 The mouth may be slightly shifted anteriorly by increase in size 

 of the anus, or by the anal tube coming to occupy the centre of 

 the tegmen, as in Batocrinus, or even to pass beyond it towards 

 the anterior margin, as in Siphonocrinus (p. 199). But the mouth 

 remains in the axis of the coil, and such forms are called " endo- 

 cyclic." In Actinometra (p. 196) the gut winds in the same way, 

 but instead of issuing immediately the first coil is completed, 

 it continues to coil, not however around the axis of the 

 mouth but around the axis of the anus. The mouth, with its 

 annular accompaniments, therefore lies between the outer coil and 

 the next one, and not in the axis of the coil ; such a form is called 

 "exocyclic." This type of coiling does not correspond to the 

 two coils of the echinoid gut, since those are formed by a loop 

 returning on itself, in the way that any tube or cord fixed at the 

 extremities is necessarily lengthened. The coil of the gut in 

 Actinometra is therefore doubly peculiar. Yet in the number of 

 its coils it finds a parallel among the Camerata. In many of these 

 (e.g. Teleiocrinus, Cactocrinus, Batocrinus, Strotocrinus, Macrocrinus, 

 Eutrochocrinus, Habrocrinus, and Dimerocrinus) the gut seems to 

 have been supported by a loose, spicular calcification of the 

 connective tissue around the axial sinus, forming a " convoluted 

 organ " not unlike the shell of Bulla (Fig. XLIV. 3). Probably the 

 oesophagus passed down the hollow axis, then the gut coiled 

 dextrally in a widening spire, and the rectum passed up outside, 

 often along a thickened rim. The number of coils was at least three 

 in a Batocrinus figured by Wachsmuth and Springer (1897, pi. v. 

 fig. 6). It is remarkable that two of their figures (ib. figs. 5 

 and 7), if correctly described, show a sinistral coil. There is no 

 reason to suppose that the coil of the gut was ever other than* 

 dextral in any class or order of Echinoderma, though Jaekel 

 (1897) has made an unconvincing attempt to prove that it was 

 sinistral in Camerata, Cystidea, and Blastoidea. 



In Bathycrinus, Bhizocrinus, and the larval Antedon, the mid-gut, 

 at the bottom of the thecal cavity, is widened into a stomach. 

 In JBathycrinus and Rhizocrinus are also interradial diverticula from 

 the outer side of the coil, supported by processes from the brachials 

 (Fig. LIIL). Such diverticula were present in the Silurian Habro- 

 crinus, if the evidence of the convoluted organ and of Angelin 

 (1878, pi. xxvi. f. 12) can be relied on. In Pentacrinus and 

 Antedonidae, and to a less extent in Bathycrinus, the gut-wall on 



