REPORT ON THE CRINOIDEA. 255 



rawsoni is shown in PL X. fig. 8. The adjacent edges of two contiguous first brachials 

 send out short processes which meet one another and rest upon the fused muscle-plates of 

 the two radials beneath, so as to cut oft' a tubular space from the body-cavity. I have 

 found nothing like this in either of the other specimens, which have lost all the visceral 

 mass together with the second and following brachials (PI. X. fig. 6). The structure in 

 question may be only accidental, or on the other hand it may perhaps have some relation 

 to the anal tube. 



The presence of the syzygy between the first and second brachials of RMzocrinus 

 renders it a matter of some difficulty to obtain entire specimens, especially of RMzocrinus 

 rawsoni. For the arms break away at this point, carrying with them the entire visceral 

 mass. This is the condition of the individuals represented in PI. X. figs. 1, 6, 8 ; while 

 fig. 20 shows the arm-bases from the second brachial onwards, and the visceral mass which 

 they enclose. Two of them have been removed so as to expose the simple digestive 

 apparatus, with the oral plates around the mouth and a relatively long anal tube. The 

 position of the genital glands in the pinnules borne by the epizygals of the third syzygial 

 pair is also well shown. 



I am strongly inclined to believe that the loss of the visceral mass and arm-bases may 

 occur and be made good during life. This appears to have taken place in the Havana 

 specimen represented in PI. X. fig. 7. Small oral plates are visible in the centre at a 

 point much below their usual level, which is seen in fig. 20 ; while the second brachials 

 are so much smaller than the first that the difi'erence is evidently due to fracture and 

 reparation, just as so often occurs on the arms of Pentacriniis and Comatula. But in 

 this case all the arms broke away together, carrying the visceral mass with them, so that 

 a new one had to be developed within the ring of regenerated arms. Not much is to be 

 seen of it, however, except the oral plates, the replacement of which is a point of 

 considerable interest. It has long been suspected that eviscerated Comatulae have the 

 power of restoring their disks ; ^ but this is the first instance of the kind that I have met 

 with in a Stalked Crinoid. 



Owing to the fact that the ring of anchylosed basals in Rhizocriniis was at first 

 regarded as an enlarged top stem-joint, the affinity between this genus and Bourgueti- 

 crinus has been supposed to be much closer than can be admitted in the light of our 

 present knowledge. For in some respects Rkizocrimis stands farther from Bourgneti- 

 crinus than even Bathycrinus does. The fossil genus Mesocrinus,^ although still but 

 imperfectly known, is probably nearer Bourgueticrinus than either of these two genera. 

 But it appears to diff'er from them in the smaller size of the upper stem- joints, a point in 

 which it resembles both RMzocrinus and Bathycrinus. In the two best known species 



1 See Marshall, Quart. Journ. Micr. Sei., 1884, vol. xxiv., N. S., pp. 525, 526. 



2 On Two New Crinoids fi-om the Upper Chalk of Southern Sweden, Quart. Journ. Geol. Soc, vol. xxxvii. p. 130, 

 pi. vi. figs. 1-7. 



