UNUSUAL FOEM OF HEMIPHOLIS. Ill 



the classification of the Ophiuroidea is at present full of anoma- 

 lies, and the admission of unusual forms into any group is beset 

 with difficulties. The naked interbrachial spaces and the paucity 

 of oral accessories (admitting, for the sake of argument, the spines 

 on the side mouth-shields to be " mouth-papillae "), and the gene- 

 ral shape and anatomy of the arms, permit of the association of 

 the species with Hemipliolis, Agass. But the great plates on the 

 upper part of the disk are not invariable in the genus, and the 

 long curved and downward projecting jaws would be abnormal to 

 it. This genus, however, is the most convenient, and therefore I 

 place the species therein, subject to the concurrence or opposition 

 of a classificatory dogma which insists upon the primary value of 

 characters relating to the very variable dermal structures. 



But the zoological position is the least important part of the 

 environment of this remarkable species. The' nature of the so- 

 called dental or " chewing " apparatus is full of interest; and its 

 consideration suggests the necessity of employing new terms and 

 of deciding the physiology of the oral structures. 



The mouth-papillae of Ophiurans, whatever may be their num- 

 ber, breadth, or length, should arise from the sides of the jaw- 

 angles ; and there are instances where they may originate at the 

 junction of the jaw and the side mouth-shield. The origin of a 

 mouth-papilla from the side mouth-shield alone is often seen, and 

 it is always in relation to the tentacle-opening close by. Ano- 

 ther mouth-papilla is said to exist high up in the jaw-angle, and 

 it is close to the first tentacular opening. It is clear, to my mind, 

 that the so-called mouth-papillae arising from the side mouth- 

 shields, and also those coming from the side of the jaw close to the 

 first tentacular opening, are more or less modified tentacle-scales, 

 and should be called tentacle-scales or spines. They may be ab- 

 solutely like tentacle-scales or sharp spines. Tentacle-scale is 

 therefore their proper name. This will restrict the term mouth - 

 papilla to its proper limit, on the lower sides of the angles and below 

 the jaw-plate. They partly cover over the lower outlet of the 

 jaw-angle, whose cavity communicates with the true oral pas- 

 sage. They are dermal structures. In the species now under 

 consideration the derm from the sides of the jaw-angles is not 

 in the form of denticulations, spinules, or angular processes, but is 

 a lamina, so closely approximated to that of the neighbouring 

 angle-side that a mere slit exists, so perfect is the closure. 

 The use of this dermal prolongation, this continuous analogue 



