of the Ophiuridse and the Echinidse. 443 



remarkable in possessing, in addition to the four arms which ema- 

 nate from the margin of the dome, and the other four arms which 

 form the framework of the mouth and oesophagus, two other arms 

 which run backwards and downwards, and also three distinct ones 

 running from the external surface of the dome, thus in all thirteen 

 arms ; moreover in the four ciliated plates which exist in the 

 former genus being here entirely absent, and in the arras (ex- 

 cepting the two supernumerary ones behind and below) being ex- 

 tremely long. Of the three peculiar arms on the dome, the odd 

 one forms a more or less elongated, frequently very long stalk on 

 the summit of the dome, as if it were the elongated axis of the ani- 

 mal. It contains a calcareous skeleton, i. e. a reticulated axis with 

 three longitudinal ridges. Opposite that foot, upon which this 

 axis rests upon the dome, it subdivides into two calcareous 

 ridges, w^hich descend within the dome and are continued into its 

 lateral arms. The three axes at the dome are not covered with 

 cilia ; the ciliated plates are also entirely absent. The cilia cover- 

 ing the lower arms and the arches between them are arranged as 

 in the previous genus. The four extremely elongated main sup- 

 ports of the dome contain reticulated calcareous axes ; the calca- 

 reous axes of the four equal elongated appendages which form 

 the oral framework and the supernumerary posterior and inferior 

 appendages are simple. The dome is much higher in this spe- 

 cies. The distribution of the calcareous ridges from the axes 

 within the dome is exactly similar to that in the previous genus, 

 especially that species in which the dome is round. Some of 

 these larvse did not exhibit any trace of the disc of the Echinus, 

 others had it on the single lesser side of the dome ; in others the 

 disc was covered with spines, and between them ambulacral pores 

 and tentacles existed. I have never seen pedicellarise in this spe- 

 cies. The spines exactly resemble those of the previous genus, and 

 become so elevated, that they project beyond the larva and the 

 animal moves them spontaneously. The calcareous skeleton ex- 

 isting in them forms a six-sided prism of lattice-work, the upper 

 ridges of which are elongated beneath the external tegument of 

 the spine into small teeth. The internal arrangement of the axes 

 in the substance of the spine is also six-rayed. The whole sur- 

 face of the disc is densely covered with these spines, and like 

 the entire larva and its appendages, they are spotted with yellow 

 and brown pigment. Its size is as considerable as that of the 

 previous genus ; the length is equal to the third or fourth part of 

 the diameter of the whole body upon which they are situated. It 

 is worthy of remark, that the disc with the spines is longish 

 oval, round, and is considerably more elongated inferiorly than 

 in the previous genus. The disc upon which the spines arc 

 situated consists of a calcareous net of lattice-work. 



