50 COXOLAMPAS SIGSBET. 



De Loriol has proposed the name of Phylloclypeus.* These discoveries 

 led me to make a renewed examination of Conoclypus Sigsbei. On opening 

 a specimen I found that it was edentate, as had been suggested by De 

 Loriol from the presence of the well-developed phyllodes (PI. XVII. Fig. 5) 

 characteristic of Echinolampas and of the edentate Conoclypus type he 

 called Phylloclypeus. On comparing the structure of the actinostoine in 

 Conoclypus Sigsbei, as seen from the interior, with that of Echinolampas, I 

 found very striking differences. As is well known, in Echinolampas Hellci 

 (PI. XV. Fig. 9, Rev. Echini) the test immediately round the actinal open- 

 ing rises slightly, in a conical shape, above the general level of the actinal 

 floor. This is also the case in E. (kjtrcssa, but in both cases the edges of 

 this conical elevation form a smooth ring round the actinostome, the cone 

 being in fact merely the turning up of the outer edges of the last plates 

 immediately adjoining the actinostome. In Conoclypus Sigsbei, on the con- 

 trary, the structure of the ring of plates round the actinostome is quite 

 similar to that described by Zittel and De Loriol in Conoclypus with 

 teeth; the processes which support the jaws, although wanting (PI. XVII. 

 Fig. 4), are still indicated by slight angular knobs, and we also find the 

 deep pits described by these authors in the interambulacral areas at the 

 base of this elevated ring. 



This structural feature is one of the most interesting found among Echini, 

 as it seems to show us the direct passage, as it were, between the edentate 

 Echini and those provided with teeth. We have no full description as yet 

 of the jaws of Conoclypus, hut. enough is known to show us how closely 

 allied they are to those of the Clypeastroids. In Conoclypus they are evi- 

 dently held in place by vertical processes, very similar to those which thus 

 far have been considered as characteristic of the Clypeastroids. With the 

 diminution in size of the jaws in these types we must expect to find genera 

 in which the supporting processes alone are left, and we may look for them 

 in the forms allied to the genus Phylloclypeus of De Loriol. The next stage 

 will be the practical disappearance of these processes, their former presence 

 being indicated by mere knobs, as in Conoclypus Sit/sh, i. until we get the 

 typical modern Echinolampas, in which the plates forming the actinal ring 

 ne only as a low cone above the general level of the actinal floor, and all 

 traces of these processes and of the interambulacral actinal pits have dis- 

 appeared. It may be convenient for the present to call this modern rep- 



* Mem. de laSocde Phys. el d'Hist. Nat. de Geneve, 1880, XXVII. 79. 



