PALJSOCRINOIDEA. 429 



rest upon the basals, and form with the first radials a ring of ten plates ; 

 while the arms, varying in number from ten to twenty, are bifurcated two 

 or three times during their course. Allied to Rhodocrinus is the genus 

 Ollacrinus (Gilbertsocrinus) of the Carboniferous Limestone. 



The genus Glyptocrinus has been commonly referred to the Rhodocrin- 

 idce, but it is now placed by Wachsmuth and Springer in the Melocrinzdce, 

 while other authorities regard it as the type of a separate family (Glypto- 

 crinides). In this genus, the turbinate calyx possesses underbasals, but 

 these are of small size, and may be quite rudimentary. The calycine 



Fig. 301. — a, Calyx and arms of Encalyptocrimts rosaceus, viewed from one side, of the 

 natural size— Devonian (after Schultze): b, Calyx oi Glyptocrinus basalts, viewed from one side, 

 of the natural size — Ordovician (after M'Coy). 



plates are ornamented with characteristic radiating ridges (fig. 301, b) ; 

 the arms are uniserial ; and the column is annulated or moniliform. All 

 the species of Glyptocrinus appear to belong to the Ordovician period. 



Family 5. Calyptocrinidce. — In the remarkable forms included in 

 this family, the calyx is regular and "monocyclic," flattened or 

 hollowed out basally, and passing superiorly into a flask-shaped 

 tegmen, which is narrowed above, and terminates in a centrally 

 placed anal aperture surrounded by regularly arranged polygonal 

 plates. The arms are, typically, twenty in number, biserial, and 

 not projecting beyond the level of the upper limit of the calyx ; and 

 they are situated between riblike processes of the upper margin of 

 the cup, or in special lateral niches formed by vertical outgrowths 

 from the wall of the calyx. The members of this family are exclu- 

 sively confined to the Silurian and Devonian formations, the prin- 

 cipal genus being Eucalyptocrinus. 



In Eucalyptocrinus (fig. 301, a), the calyx is inverted upon itself, the 

 calycine cup being deeply concave at its base, so as to look like the bot- 

 tom of a wine-bottle. Within this basal funnel are situated the four small 

 basals, which are succeeded by five large primary radials. These are 

 strongly bent, one-half of each passing up into the basal funnel, while 

 the other half appears on the lower and lateral aspects of the cup. Two 

 other rows of radials succeed these, the tertiary radials being unusually 

 large, and each supporting the bases of two arms. The interradial 



