. The Cambridge natural history. Zoology. 598 ECHINODERMATA CYSTOIDEA the two foregoing classes. Formerly this class was a lumber- room in which were placed all primitive irregular Pelmatozoa. The labours of Jaekel'' have, however, dispelled the mist which enveloped this group, and in his monograph all that can be extracted both from superficial examination and dissection of these fossils is contained. It seems possible to the present author that the class may eventually require to be divided into two, corresponding to the two main divisions which Jaekel recognises, viz. Dichopokita, with pect
. The Cambridge natural history. Zoology. 598 ECHINODERMATA CYSTOIDEA the two foregoing classes. Formerly this class was a lumber- room in which were placed all primitive irregular Pelmatozoa. The labours of Jaekel'' have, however, dispelled the mist which enveloped this group, and in his monograph all that can be extracted both from superficial examination and dissection of these fossils is contained. It seems possible to the present author that the class may eventually require to be divided into two, corresponding to the two main divisions which Jaekel recognises, viz. Dichopokita, with pectinated rhombs, and DiPLOPOHiTA, with diplopores. The pore-rhombs of the Dichoporita (indicated in Fig. 277 by the small parallel lines crossing the boundaries of the plates) mouth Fig. 277.—Echinosphaerites mt/rantiwu. A, from above ; B, from the side ; C, ueigh- bourhood of mouth, enlarged, avib. Ambulacra! groove with side-plates and cover- ing plate ; mad, madreporite. The short parallel lines across the sutures are the "; (After Zittel.) were, according to Jaekel, nothing but a series of folds of thin integument projecting into the interior, the outer opening of which in most cases adhered in the middle, leaving two pores connected by a groove. The inner boundaries of the folds are sometimes preserved, but in many cases they were entirely devoid of calci- fication, and so were lost. The radial vessels either branched a great deal, giving rise to a multitude of fingers, or, as in Uchino- sphaerites (Fig. 277), there were a few long fingers supporting a reduced number of radial canals. In some cases the calyx can be analysed into a regular series of cycles of plates, consisting of basals, orals, and three intervening whorls, thus including one more ring than the calyx of Crinoidea. Jaekel regards this as a primitive arrangement, believing that the irregularity seen in Ji'chinosphaerites is secondary. This is a doubtful hypothesis. ^ Stammesgeschi
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