/)84 MR. W. BATESON ON ABNORMAL [JuilC 1", 



apex of this horn is a small circulai' pit which is apparently closed 

 oy membrane. The other appendages are normal. 



A considerable number of cases similar to the above have been 

 collected, especially by Kraatz, Mocquerys, and Jaj'ne, 



I\'. — Antedon rosacea with Abnormal Repetition of the 

 Brachial Structures. 



This individual was found amongst a number of other specimens 

 of A. rosacea collected by a party that had been dredging for the 

 Plymouth Laboratory in the Hamoaze, near Beggar's Island. 



In normal individuals of this species the arms after leaving the 

 radial plates do not again divide, but are continued to their ends as 

 a single row of brachial plates, which bear pinnules on either side 

 alternately. The present specimen, however, bears two arms, 

 which, after being continued normally for a certain distance, break 

 up into several secondary arms. Tlie diagram (fig. 4, A) shows the 

 relation of these two varying arms (lettered 6^ and «,) to the mouth 

 and anus. It is seen, therefore, that they are symmetrically placed. 



As I am inexperienced in the use of Crinoid terminology, I sent 

 this specimen to Dr. P. H. Carpenter, who has very kindly supplied 

 the following description of it :■ — 



" The abnormal arms of this remarkable specimen are symmetri- 

 cally placed as regards the mouth and anus, being the posterior arms, 

 6j and e^, of the two anterolateral rays. The arm b^ has been 

 regenerated at the syzygy in its 15th brachial. But the pinnule on 

 the new epizygal is on the same side (abradial or outer) as that on 

 the 14th brfichial, 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 twelve pinnules alternate regularly on oppo- 

 site sides, those of the 19th and 27th brachials having much enlarged 

 basal joints. That on the 28th brachial is considerably larger than 

 its predecessors and more like a bifid armlet. It commences with 

 five large joints, the last of which bears two pinnules, the one con- 

 tinuing the main axis being rather stouter than its fellow. The 

 29th brachial is a syzygy and its epizygal axillary. The abradial 

 or outer facet bears an arm, of which some 75 joints remain. It 

 has pinnules on the 2nd and 4th, the latter of which is a syzygy ; 

 but there is none on the 3rd, which would normally be a syzygy 

 and bear a pirinule. On the larger, adradial, facet of the axillary 

 29th brachial is another axillary (30th br.), but without a syzygy. 

 One of its facets bears the continuation of the primary arm, on the 

 next joint of which (31st br.) is an abnormal trifid armlet with 

 three enlarged basal joints, the second being a syzygy with a pin- 

 nule-stump on the epizygal, while the fourth bears two pinnules. 

 The 32nd brachial is again axillary with a syzygy, its epizygal 

 bearing two subequal arms of some 60 joints each. The second 

 joint of the left-hand one which continues the primary arm has a 

 bifid pinnule with its basal joints enlarged, and the following pin- 

 ^^les alteraate reg\ilarly on opposite sides. The arm borne on the 



