ON CAKBONIFEROTJS ENCRINITES. 485 



mammillaris normally pentagonal. Careful observation will always 

 show which is the rule. 



The grounds on which I believe that Phillips' genus Gilbertsocrinus 

 must be retained are, that all the specimens of hursa^ mammillaris, 

 calcaratus and two or three new species which I have examined, 

 agree in the very peculiar structure of the brachials and the arm- 

 bases The first brachial is hexagonal ; the second also hexagonal, 

 but channelled at top and leading into an orifice which opens into 

 the perforation through the arms : the arm-bases are set on at right 

 angles to the surface of the body, and form a kind of roof over the 

 above mentioned orifices, f Plate VIL, Jigs. 11, 12. J The orifices 

 are well seen in Phillips' detailed drawing of hursa. The axillary 

 plates also between the brachials are developed to a much greater 

 extent than in any other genus, and the irregularity of the plates 

 above the second brachial, surrounding the orifices and the arm 

 bases, is also characteristic, f Plate VIL, fig. 12. J 



The difi'erence between this complicated arrangement and the 

 straight-forward arrangement of the brachials in the true 

 Ehodocrini, e.g., verus, verisimilis, and granulatus, is quite sufficient 

 to establish a generic difi'erence between these forms, especially as 

 these orifices are not found, so far as I am aware, in any other genus. 

 The channel at top of the second brachial is fitted in one of 

 Mr, Rofe's specimens with a small semicircular plate which he calls 

 a fillet — it is figured in the Geol. Mag. vol. 2. Mr. Eofe there 

 suggests that these orifices are ovarian, but it seems to me more 

 probable that they are for the purpose of admitting water into the 

 interior. Eecent researches on the living crinoids have established 

 the fact, that the cilise of the arms set up a current of water which 

 travels down the groove in the arms, passes also in grooves over the 

 surface of the dome, then enters the cavity of the body, and passes 

 through a membrane which filters off the minute organisms which 

 constitute the food of the crinoid, and, finally, passes out through 

 the proboscis. This latter is, thus, simply an efferent tube which 

 serves to carry to a distance from the arms, the water which has 

 already passed through the body. ' 



