222 NATURAL HISTORY BULLETIN. 



Only one species of this group has been described from 

 Atlantic waters, viz, Actinometra lineata P. H. Carpenter, 

 which has been dredged in the Caribbean Sea, and off the 

 coast of Brazil, at depths of from 7 to 88 fathoms. It is a con- 

 siderably smaller species than ours, which is one of the largest 

 of the genus, and ours does not possess the dark medio-dorsal 

 line of that species; the form of the brachials is also different. 

 From Actinometra fimbriata and its allies of the Indian 

 Ocean it differs in the number and size of the cirri, and in the 

 form of the brachials. 



From all it differs in the presence of plated ambulacra. 



Carpenter mentions without description (Chall. Rep. Comat. 

 p. 316), under the name Actinomctcr discoidea, another species 

 of this group, dredged by the "Blake" at 88 to 118 fathoms. 

 The only character of it which he specifies is that it has the 

 "arm-joints quadrate," which is the case with our species for 

 the first six or seven brachials, but above that they are very 

 different. 



The presence of alternating covering plates in the ambulacra 

 is really the most remarkable feature of this peculiar form. 

 This is very conspicuous, and may be readily seen at several 

 places on the photographic figures 2 and 3 on the accompanying 

 plate as well as in the drawings of portions of arms and pin- 

 nules, figs. 4 and 5. The absence of a plated ambulacral skeleton 

 on arms and pinnules has hitherto been regarded as one of the 

 most striking characters of Actinometra. In this structure it 

 differs from Aniedon, and all the stalked crinoids. No other 

 crinoid, recent or fossil, was known to be thus constructed 

 until it was found, as I have lately pointed out, in the remark- 

 able Cretaceous genus Uintacrinus (Memoirs Museum Com- 

 parative Zoology, Harvard, Vol. XX V, No. 1.) Our species 

 has the other characters of Actinometra in a marked degree. 

 No one who has any acquaintance with these crinoids would 

 hesitate to refer it to this genus, on the first glance at the 

 exocyclic disk and combed pinnules, which are thoroughly 

 characteristic. 



