22 On the Anatomical Nomenclature of Echinoder ms. 
by Fewkes ; but he would have been more in accordance with 
the rational terminology now current if he had used inter- 
mediary or interambulacral for interbrachial*, and had adopted 
Muller’s use of adambulacral. 
On p. 105 of his last' paper j* we read, u The plates in the 
Echinoids called adambulacrals which lie between the system 
of plates generally known as ambulacral are regarded as the 
same as the marginal plates of the starfish.” This passage 
can only refer to the plates which are always called inter- 
ambulacrals in the test of an Urchin, and I have been unable 
to discover that any author, except Fewkes, has ever called 
them adambulacral. Ludwig J, however, has pointed out 
that the ambulacral plates of an Urchin are in all probability 
homologous with the adambulacrals of a Starfish, and in his 
diagram of the skeleton of an Echinoid he marks these plates 
u Adambulacralia (sog. Ambulacralia).” Fewkes, on the other 
hand, speaks of u the so-called adambulacrals of sea-urchins ” 
when he means the interambulacrals, auet., although no pre- 
vious writer has employed the term in this sense, so that there 
was no reason for Fewkes to have done so. He accepts 
Ludwig’s homology of these interambulacral plates (adambu- 
lacrals, Fewkes) with the marginals of the Starfish, as shown 
in the following table, copied from p. 106 of his memoir: — 
Starfish. 
Sea-Urchin. 
1. Ambulacral rafters. 
2. Peripheral ambulaerals §, gene- 
rally called adambulacrals. 
3. Marginals. 
1. Wanting. 
2. Ambulaerals. 
3. Adambulacrals. 
But he also remarks in a footnote, u The homologies here 
presented are essentially the same as those already published 
by Ludwig as far as the relationship between the ambulaerals 
of the starfish and the adambulacrals of the sea-urchin is con- 
cerned.” There seems to be something wrong here, for it is 
clear that the adambulacrals of an Urchin cannot be homolo- 
gous both with the ambulaerals of a Starfish (footnote) and 
also with its marginal plates (table). 
It may be that a clerical error has been committed, the 
prefix ad being put in the wrong place in the footnote, and 
* This term is not particularly applicable in the ease of Goniaster and 
similar forms. 
t Proc. Boston See. Nat. Hist. 1889, vol. xxiv. p. 105. 
X “ Entwicklungsgeschichte der Asterina gibbosa , Forbes,” Zeitschr. f. 
wiss. Zool. 1882, Bd. xxxyii. p. 73. 
§ r I hese “ peripheral ambulaerals ” are also called interambulacrals by 
Fewkes, and in his figure on p. 99 they are lettered ad, Adambulacrals ! ! 
