128 SMITHSONIAN INSTITUTION 



described species and by a like number in Britain and continental Europe at corresponding 

 Silurian and Devonian horizons. 



I take the chief comparative measurement of general dimensions in this genus at the 

 apex of the axillary primibrach, as in some species the arms infold before the next bifurca- 

 tion, and in many specimens they are not preserved. All measurements are in millimetres. 

 To facilitate comparison, I have arranged the Silurian and the Devonian species in separate 

 groups. 



The Species of Lecanocrinus 

 Silurian Species 

 I. IBB protuberant. 

 Surface smooth. 



RR large. Anal x large, and rising high above radials. 



BB large. Crown ovoid L. macro petalus. 



Crown pyrif orm L. solidus. 



Surface ornamented, calyx plates thick. 



RR large. Anal x short and wide, crown subglobose L. pusillus. 



RR small. Anal x long and narrow, crown ovoid L. billingsi. 



II. IBB not protuberant. 

 Base not concave. 



RR large, IBr short. Anal x not projecting high. 

 Anal x truncate. IBB visible in side view. . 

 Surface fine pitted network. 



Calyx walls thin L. facietatus. 



Surface coarse granules. RR smaller. 



Calyx walls thick L. lindstromi. 



Anal x acuminate. IBB not visible in side view. 



Calyx walls thin L. pisiformis. 



RR small. IBr long, increasing in width upward. 



IBB visible. Base rounded L. bacchus. 



Base truncate. Br angular L. angulatus. 



IBB invisible. Base truncate, involving part of BB L. meniscus. 



Base concave. 



BB large. RR small. 



IBB large, radiating ridges on plates L. ivaukoma. 



Devonian Species 

 IBB not protuberant. 



Base excavate. Anal x not projecting. 



Calyx pentangular L. roemeri. 



Base truncate, calyx circular. 



Anal x little projecting, surface coarsely granular L. soyei. 



Anal x projecting over half above RR L. magnaradialis 



