316 A. E. Verrill — North American Ophiuroidea. 



included in Amjyhiura four groups that differ in their mouth-parts 

 so widely that I have been led to separate them as genera, he natur- 

 ally admitted the same variations in the mouth-parts of Ophiocnida. 

 In fact we find in this group, as he finally left it, four divisions cor- 

 responding to the four divisions of Amp>Mura in structure of the 

 mouth. They should be separated, therefore, if those of Amphiura 

 are to be separated. 



When originally constituted the genus included only two species. 

 These are much alike and agree in mouth-parts. They have three 

 subequal, true oral papillae, arranged as in the division of Am- 

 phiura that I have called Amphiodia^ to which they are in every 

 way closely allied. It is, in fact, rather doubtful whether these two 

 groups might not be united into a natural genus. In that case the 

 variations in the covering of the disk might be considered as of 

 merely sectional value. 



But if we restrict Op)hiocnida to the species having the characters 

 of the ty2:)es, they form a natural and easily recognizable group, 

 which it is well, so far as known at present, to keep distinct. Mr. 

 Ljungman gave the name Ophiocnidella to this typical group. 



The second group, of which 0. Putnami may be taken as the 

 type, agrees with typical Amphiura in its mouth-parts, having but a 

 single true oral-papilla, placed at the tip of the jaw, on each side, 

 and one or two pairs of oral tentacle-scales at the distal corner. I 

 have been inclined to consider this as a subgenus of Amphiura^ for 

 which I have proposed above (p. 307) the name Amphiocnida. It is, 

 at any rate, very closely related to Amphiura. A study of its in- 

 ternal skeletal plates may hereafter show distinctions of more evi- 

 dent generic value. 



The third group includes, so far as I know, only 0. ahnormis 

 Lym. This agrees so completely in its mouth-parts, spines, etc. 

 with typical AmphiphoUs^ that I do not hesitate to unite it with 

 that genus, considering the sparingly spinulose disk as merely of 

 sectional value. (See p. 313.) 



Another group, Ainp)hiUmna^ having 0. oUvacea as its type, has 

 more numerous oral papillae and arm-spines, and a genei-ally robust 

 structure quite unlike the typical forms. Although corresponding 

 with Amp?iioplus in the number of oral papilhe, this group seems 

 to have special characters worthy of generic rank. 



The following synopsis will give the principal characters of the 

 three more important divisions discussed above, and of most of the 

 described species : 



