258 n. N. MOSELEY. 



up into numerous fragments when handled^ though the frag- 

 ments still hang together and the outlines of the plates remain 

 unimpaired. The whole of the plates composing the pharyngeal 

 armour are attached side by side^ as in other Dendrochirotse 

 by membrane, and not articulated to one another. 



The present specimen is especially remarkable for its large 

 size. In Molpadia chilensis a somewhat similar pharyn- 

 geal skeleton was described by Johannes Muller/ and a con- 

 siderable number of Dendrochirotse of different genera possess 

 a calcareous pharyngeal skeleton composed of separate plates, 

 iu addition to the usual simple ring, but in all of these the 

 pharynx is extremely small, scarcely more than one fifth of the 

 size of the present example, or smaller still, and the plates of 

 which the pharyngeal portion of the skeleton is made up are 

 minute microscopic objects, and appear to vary more in form 

 and be arranged with less regularity than is here the case. 



The largest pharynx of the kind hitherto described appears 

 to be that of Thyonidium Schmeltzii of Dr. Hubert 

 Ludwig,^ in which it attains a length of 1^ cm., the entire 

 length of the animal itself being only 6 cm. 



The pharyngealia are commonly treated of as merely elonga- 

 tions of the annularia in a posterior direction, accompanied by 

 their subdivision into plates,^ and some facts concerning the 

 forms of the annularia in various species seem to point in this 

 direction, but in a pharynx such as the present, in which the 

 pharyngealia are so highly differentiated and regularly disposed, 

 it is at least convenient to distinguish clearly between them and 

 the very different annularia which appear to be in themselves 

 adequate homologues of the calcareous ring of most Holo- 

 thurians. Only embryological evidence can satisfactorily de- 

 termine whether the series of pharyngealia occurring in forms 

 such as the present are really in origin outgrowths of a primitively 

 simple annulus, or, as appears possible, additional independent 



^ J. Miiller, • Ueber den Bau dcr Echiiiodermen,' Taf. iv, fig. 1. 



2 H. Ludwig, ' Arbeiten aus dem zoolog. zootom. Institut iu Wurzburg/ 

 ii Bd., S. 94. 



3 Semper, 1. c, p. 159. 



