16 



ANNAL^< NfJW YORK ACADEMY OF SCFENCES 



Cactocnnus co'lalu.s var. spiiiolentaciilns on the same plate shows the 

 close similarity between the amis of the two species throughout their 

 entire development. Teleiocrinus. umbrosuH seems to have been developed 

 from Cactocrinns ccelatus var. spinotentaculus by an increase in the size 

 and thickness of the calyx plates and a more frequent branching of the 

 arms near their base, which produced the expanded rim of the calyx char- 

 acteristic of Teleiocnntis. 



^ 

 ^ 



Te/e 



/ocjinus i/moroiui 



h 



C. coc/olas 



rt I , ■ I , spinotcnl o coJus 



6. cfe nticu/ati/s 





^5 





C opus c L//as C- retlcu/atus 



C.pla tubro ch i aius 

 C.thet/s C. fjoccatt/s 





C. ?7Tl//t/6/OC/^/oh/S 



C. J/?rJoI)/ oc/?/Q- 

 tus 



C prohoscfcfa/is 



Smooth armed ancesio? 



Fi(!. I. —Relationship of species of (.'actocriniis and Teleiocrinus 



Teleiocrinvs allhcca (Hall) is represented in the collection of the Mu- 

 seum of Comparative Zoology by only one specimen which preserves the 

 arms. From this, it appears that the numerous anns are flattened dorso- 

 ventrally at the base but become larger and cylindrical in form above. 

 This suggests that we have in Teleiocrinus althcea an actual advance in 

 evolution expressed in a simplification of form rather than in greater 

 complexity. 



The general relations of the species mentioned above are expressed in 

 'diagrammatic form in Fig. 1. 



