PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 201 



this species in connection with his work on those of other crinoids, finds that the radianal 

 appears before the right posterior radial, which forms to the right of it, in exactly the 

 same way in which these two plates appear in Promachocrinus. Its formation there- 

 fore is not delayed until the appearance of the elements of the IBr series as was sup- 

 posed by Sir Wyville Thomson. 



Furthermore, Dr. Mortensen (1920) calls attention to the fact that Professor 

 MacBride (1914) had correctly identified as infrabasals a plate Thomson designated 

 as the centrodorsal in a reproduction of one of his figures, though Thomson had made 

 no mention of them hi his text. Mortensen also states that infrabasals are constantly 

 present in this species, usually two larger and one smaller, lying in the usual place about 

 the topmost columnal. 



Abnormal specimens. With four rays: P. H. Carpenter (1888) records a 4-rayed 

 specimen in his collection, the anterior ray being absent; and Chadwick (1907) has ob- 

 served several 4-rayed individuals, presumably from the vicinity of Port Erin. 



With nine arms: W. B. Carpenter (1866) described and figured a 9-armed specimen 

 in which on one of the rays the IBr 2 is absent so that the first brachial immediately 

 follows the IBrj, which is of about twice the normal length. 



With eleven arms: W. B. Carpenter (1866) described and figured an individual 

 with one IIBr series of 2 segments and 1 1 arms. 



With twelve arms: Dendy (1886) described in great detail and figured a specimen 

 with two IIBr series of 2 segments and 12 arms; one of the IIBr series was on the 

 posterior side of the left anterior ray, the other being on the anterior side of the right 

 posterior ray. The individual, which is preserved in the British Museum, is unusually 

 large. 



With palmate arms: Professor William Bateson secured a specimen with palmate 

 arms which had been dredged in the Hamoaze, Plymouth, near Beggar's Island together 

 with a number of other normal ones. This he turned over to P. H. Carpenter for 

 description. The latter (1890) writes that the two abnormal arms of this remarkable 

 specimen are symmetrically placed as regards the mouth and anus, being the posterior 

 arms of the two anterolateral rays. The arm 6 2 has been regenerated at the syzygy in 

 its 15th brachial (i.e., at brachials 18+19 by modern terminology where syzygies are 

 counted as two brachials), but the pinnule on the new epizygal is on the same side 

 (the outer) as that on the preceding 14th brachial and not opposite to it as would 

 normally be the case, so that there are two pinnules in succession on the same side of 

 the arm. The next 12 pinnules alternate regularly on opposite sides, those of the 

 19th and 27th brachials having much enlarged basal joints. That on the 2Sth brachial 

 is considerably larger than its predecessors, and more like a bifid arndet. It commences 

 with five large segments, the last of which bears two pinnules, the one continuing the 

 main axis being rather stouter than its fellow. The 29th brachial is syzygial, with an 

 axillary epizygal. The outer facet bears an arm of which some 75 segments remain. 

 It has pinnules on the 2nd and 4th, the latter being syzygial, but there is none on the 

 3rd, which would normally be syzygial and bear a pinnule on its epiz3'gal. On the 

 larger, internal, facet of the axillary 29th brachial is another axillary (30th brachial), 

 but without a syzygy. One of its facets bears the continuation of the primary arm, 

 on the next segment of which (the 31st brachial) is an abnormal trifid armlet with 

 three enlarged basal segments, the second being syzygial with a pinnule stump on 

 the epizygal, while the fourth bears two pinnules. The 32nd brachial is again 



