Anatomical Nomenclature of Echinoderms. 17 



strict sense in wliich the term is to be used for the future 

 should surelv l»e that in which it was most generally used in 

 the past. This is very far from being the case with Lov^n'a 

 specialization of the term costals, as will be seen from the 

 preceding table ; and as his proposal has not been generally 

 adopted by Echinologists, I think there can be no harm in 

 employing Miller's name for plates which do lie in the 

 direction of the rays of Crinoids, and were always called 

 costals by him when not described as arm-plates, viz. those 

 commonly known as the second radials. This being granted, 

 it naturally follows that the axillary or third radials, the 

 scapula? of Miller, should be called the second costals; and 

 these terms will be employed for the future by Messrs. 

 AVachsmuth and Springer, leather, and myself. Further- 

 more, in genera like Metocrinns and Par isocr inns, in which 

 there may be four or five joints between the radial and the 

 first axillary above it, the whole series, including the axillary, 

 will in future be called the costals. 



The use of this term also simplifies matters in another way. 

 I pointed out in 1877 *, and have done so frequently since, 

 that the first two joints beyond every axillary of a multi- 

 brachiate Xeocrinoid are nearly always united, whether by 

 syzygy or by bifascial articulation, in tiie same manner as the 

 second and third radials. Now, however, we can say more 

 briefly that there is generally the same mode of union between 

 the first two free brachials and the first two distichals and 

 palmars &c., when present, as between the first two costals. 

 Thus, among the Palajocrinoidea this union is a syzygy in 

 Graphiocrinus and Scytalocrinus. The same rule holds good 

 in Encrinus (syzygy) and in Apiocrinus^ Miller icrinus, and 

 Batliycrinus (articulation). Five of the eight recent species 

 of Peniacrinus have the two costals, distichals, and palmars, 

 and the first two free brachials respectively united by syzygy, 

 while there are bifascial articulations between the two costals 

 and the first pair of joints beyond them in each of the other 

 three species. Some of the tossil Pentacriuidse present indi- 

 cations of the same regularity, and it is also traceable in Meta^ 

 crinus^ though to a less extent, owing to its larger and more 

 variable number of costals ; and this is probably also the case 

 in the Paheocrinoids with a similar character. 



It is among the Comatukcj however, that the regularity in 

 question is most marked. Among the 120 species of Antedon 



• " On the Genus Actinometra, Miill., with a Morphological Account 

 of a new Species from the Philippine Islands," Trans. Linn. Soc, 2nd ser. 

 Zool. vol. ii. p. 22. 



Ann. (f; May. N. Hist. Ser. ^. Vol. v\. 2 



