354 



THE CRIXOIDEA CAMERATA OF NORTH AMERICA. 



length of the arms, rise only to a certain height, and are not closed from 

 above. The plates, as a rule, are highly ornamented, strongly nodose, or 

 extended into long spines. The dorsal cup is constructed of the same num- 

 ber of plates, and arranged in exactly the same manner as in Eucahjjitocrinun ; 

 generally, however, the basal concavity is wider, and 

 only partly filled by the column. In the construction 

 of the ventral disk also, the t\YO genera have close 

 affinities ; the plates in both forms consist of four 

 rings, and in both of tliem the first ring is coTuposed 

 of twenty plates, the second and third of four ; but 

 ''!jf tlie fourth ring contains but four plates instead of ten. 

 and these have no wing-like extensions at their outer 

 faces ; the upper parts of their arms are free, and rest 

 directly against the walls of the anal tube. The parti- 

 tion walls, of which there are twenty in this genus. 

 ^ „. . are restricted to the plates of the first rinff, and rise 



Fig. ]7. Calhcnnus. Sideview ^ ^' 



of calyx, showing the rudi- but little abovc their general hei<rht, never touching 



mentary partitions. '" 



« = radiais; /= costal,; //= ^^e plates of the secoud ring. Five of the partitions 

 distichais; i4r = interbrachi- are Supported by the interbrachials, five by the inter- 



als; !d = interdistichals; irP _ _ ^ '^ "^ _ ' •' 



= interradiai partitions; ivp distichals ; the remaining ten are interposed between 



partitions ; . 



the ten others, and rest upon the edges of two palmars. 

 These latter partitions are formed b_y wing-like exten- 

 sions from the ten smaller plates of the first ring; 

 they rise to the same height as the others, and separate 

 the two arms wliich in Eiicahjptocriuus occupy the 

 same compartment. The plates of tlie second and 

 third rings either are flat, the general curvature excejited, or they show 

 some inclination to forming faces of attachment for partition walls. The 

 four plates of the upper ring constitute the upper end of the anal tube, 

 wliicli gi-'uerally has a quadrangular opening. Arms robust throughout, 

 closely folded, and composed, from the second or third plate up, of two 

 rows of transverse pieces. The partitions by which they are separated 

 rarely extend up liighor than to one third the length of the arms. Column 

 round ; the axial canal of medium size and pentangular. 



Distribution. — The greatest number of species occurs in the Upper Silu- 

 rian of Gotland, and there are one or two at Dudley, England. The genus 

 is represented in America by four species in the Niagara group. 

 Callicrinus costatus (Hisinger) is the type of the genus. 



= interdistichal 

 ly'P = interpalmar partitions; 

 i = the first or lower ring of 

 plates in the tegmen, com- 

 posed of ten large and ten 

 small subtrigonal pieces; 2 = 

 the plates of the second ring, 



3 = those of the third ring, 



4 = the plates of the fourth 

 ring. 



