182 PROF. p. MARTIN KUNCAN ON THE 



The shape of the so-called auricles of the Cidaridee differs from 

 that of the other Echiuoidea, and the construction of the pact 

 in Discoidea differs also. No ear is like unto any one of these 

 structures, and they have nothing whatever to do with hearing. 



Very frequently the arch of the processes is incomplete, and 

 then there is no possible similarity between them and the out- 

 lines of an ear. 



It is proposed to discontinue the term auricle. No definite 

 name has been given to the ridge-like plate which connects the 

 so-called auricles together, and which really is of as much 

 importance as the processes, which arch more or less over the 

 ambulacra. 



The whole of the structures of the test which give attachment 

 to the muscles of the jaws require a name, and that of the 

 perignathic girdle seems to have some useful qualities. 



The girdle is, when fully develoj)ed, continuous, and consists of 

 arched processes and intermediate ridges. The discontinuity 

 may be slight or very decided. 



The Cidaridee differ entirely in the arrangement of their jaw- 

 muscles, so far as attachment to the test itself is concerned, from 

 the other dentate regular Echinoidea, and the solid so-called 

 " auricles " are parts of the interradia. There are no ambula- 

 cral processes for the retractor muscles, and therefore the girdle 

 is discontinuous. 



In Discoidea there is a continuous girdle without arches, 

 although the homologues of the processes exist *. 



The terms ambulacral process and that of mnbulacral arch 

 should replace the terms " auricle " and " auricular arch." In 

 speaking of the jaws and their accessories for muscular attachment, 

 the word process or arch will suffice ; and the term interradial 

 ridge may be employed, with or without the word interradial, to 

 distinguish the ridge-like structure which unites the ambulacral 

 arches and gives attachment to the protractores and radiales. 



II. The Perignathic Gtirdle of the Cidarid^. 



A small but well-developed specimen of Dorocidaris papillata, 

 Leske, presented the aspect of the discontinuous perignathic 



* The anatomy of the test of Discoidea cylindrica will foi-m the subject of a 

 future communication to this Society. 



