430 



PELMAT0Z0A. 



plates are developed in a most singular manner, so as to form a series of 

 five linear, clavate processes, which separate and support the arms ; five 

 other precisely similar processes being borne by the axillary radials. 



The arms thus come to lie in deep grooves 

 or niches in the sides of the calice, the 

 upper surface of which they do not reach. 

 The upper surface is completely vaulted 

 over, and is mainly formed by the upper 

 ends of the ten interbrachial processes 

 just spoken of, in the centre of which is a 

 small circular anal aperture, surrounded by 

 five or more plates. The species of Etica- 

 lyptocrinns are found in the Silurian and 

 Devonian rocks ; and the Silurian genus 

 Hypanthocrinus differs principally from the 

 preceding in the fact that the base of the 

 calyx is not funnel-shaped. The Silurian 

 genus Corymbocrinus (fig. 302) has been 

 likewise placed in the neighbourhood of 

 Eucalyptocrinus, but is now considered by 

 Wachsmuth and Springer as belonging 

 rather to the family of the Actinocrinidcp. 

 In this genus the calyx resembles that of 

 Eucalyptocrinus in having a deep funnel- 

 shaped depression at its base, but the 

 arms are long and much divided. Lastly, 

 the genus Callicrinus, also Silurian, is in 

 most structural features closely allied to 

 Eucalyptocrinus, and appears to represent an earlier phase in the devel- 

 opment of the family. 



Family 6. Crotalocrinidce. — In this small and remarkable family, 

 the calyx is " dicyclic," with small underbasals and large basals. 

 The arms are uniserial, without pinnae, but furnished with numerous 



Fig. 302. — Calyx and arms of 

 Corymbocrinus Polydactylies. Wen 

 lock Limestone of Britain. (After 

 M'Coy.) 



Fig. 303. — A, Calyx and arms of Crota 7 ocrinus Loveni, cut across to show how the arms 

 are rolled up ; B, A portion of the network formed by the arms, enlarged. Silurian. (After 

 J. Muller.) 



branches, by the coalescence of which they become more or less 

 extensively connected with one another laterally, generally forming 

 wide, inrolled, foliaceous expansions. The anus, so far as known, 

 has the form of an excentric, proboscidiform, plated tube. The 



