288 CYSTOIDEA, BLASTOIDEA, AND HOLOTHUROIDEA. 



Apiocystites, Codaster, and Callocystites, arms were present, but 

 they were bent backwards and immovably soldered down to 

 the surface of the calyx. The arms spring in these cases 

 from the apex of the calyx, and are anchylosed by their 

 dorsal surfaces to the body. On their ventral surfaces the 

 arms are grooved by furrows which clearly correspond with 

 the brachial grooves of the Crinoids, and on each side of 

 these grooves is a row of pinnulse. In one or two cases 

 there is only a single row of pinnules, and the arm seems to 

 have been fastened to the calyx by one of the lateral sur- 

 faces, instead of by the dorsal surface. In one Cystidean 

 only (viz., Comarocystites punctatus, Billings), are there free 

 arms as in the true Crinoids ; but further researches will 

 doubtless show that these appendages existed in other species 

 as well. In Comarocystites, however, the arms differ from 

 those of the Crinoids in being only four in number, in not 

 subdividing (though they carry lateral pinnae), and in arising 

 directly from the summit of the calyx. 



Upon the upper surface of the calyx in the Cystideans are 

 two, or sometimes three, apertures, the functions and nature 

 of which have given rise to considerable controversy. The 

 best known of these is a large opening which is pierced in 

 one side of the calyx, usually near the middle of the body, 

 but sometimes approximated to either the apex or the base. 

 This aperture is mostly defended by a " valvular pyramid ; " 

 or, in other words, by a series of small plates, arranged in a 

 pyramidal manner, and serving for the closure of the open- 

 ing. Much difference of opinion has prevailed as to the true 

 nature of this orifice. Von Buch believed that it was an 

 " ovarian aperture ; " Mr Billings regards it as discharging 

 the functions of both the mouth and anus ; whilst Sir 

 Wyville Thomson, Mr Salter, and other high authorities, 

 regard it as being the anus, and as corresponding with the 

 proboscis of the Crinoids. That it is not an "ovarian orifice" 

 may be regarded as certain, so that the question is narrowed 

 to its being the anus alone, or an " oro-anal " orifice. In 

 the living Leskia mirabilis, one of the Sea-urchins, both the 

 mouth and vent are closed by converging triangular valves, 

 which doubtless correspond with the " pyramid " of the 



