NIAGARA FALLS AND VICINITY I49 



side plates pass insensibly into the plates of the ventral (upper) side. 

 In the center of the dorsal side, however, a regular series of basal 

 plates exists, which rest on the stem or column. 



The mouth is indicated by a central or subcentral aperture on 

 the upper (ventral) surface, and is sometimes covered by small 

 plates. From it radiate from two to five simple or branching 

 ambulacral grooves, which are also frequently roofed over by plates. 

 The anal opening is situated eccentrically and frequently closed by 

 a valvular pyramid. 



The calyx plates in most cystoids are perforated by pores or fis- 

 sures. These are often arranged to form lozenge-shaped or rhombic 

 figures, the pore rhombs, which are disposed one half on each of two 

 adjoining plates, while the line of suture between the plates forms 

 either the longer or the shorter diagonal of the rhomb. The 

 pores of opposite sides of the rhomb are united by perfectly closed, 

 straight ducts, which pass horizontally across the line of suture, 

 and produce a transversely striated appearance ( C a r y o - 

 c r i n u s , fig'. 46). These striate rhombs are generally visible only 

 in weathered specimens. They may be present on all plates or only 

 on a few. In Callocystites and other related genera, the 

 pore rhombs are reduced to pectinated rhombs, which are few in 

 number, and each separated into two distinct parts, lying on con- 

 tiguous plates (fig. 47). These structures have probably a respir- 

 atory function. 



The arms are feebly developed in the cystoids and often but few 

 in number. They are simple, consisting of a single (uniserial) or 

 a double (biserial) row of plates, and possess a ventral groove, 

 protected by covering plates. 



Genus caryocrinus Say 



[Ety. : y.dpoov , a nut; zpivov^ lily] 



(1825. Acad. not. sci. Phil. Jour. 4:289) 



Calyx composed of a moderate number of plates arranged in a 

 hexamerous manner, and with the base composed of two cycles 

 of plates (dicyclic). Lowest (infrabasals) four, unequal; followed 

 by a second row of six basals, which alternate in position with 

 those of the preceding and succeeding cycles. Third cycle of eight 

 plates of which six are regarded as radials, the others as interradials 

 (Carpenter). Ventral surface formed of six or more small pieces. 

 All plates of the calyx furnished with pore-rhombs; the summit 

 plates without perforations. Mouth and ambulacral grooves below 

 the ventral plates or tegmen. Anal opening protected by a valvular 

 pyramid, and situated on the outer margin of the ventral surface. 

 Arms, 6 to 13 in number, situated on the ventral margin, and 

 relatively feeble. Stem long, composed of cylindric segments. 



