Mr. Say on Crinoidea. 313 



correct the characters of that genus agreeably to the discoveries 

 of the ingenious Miller, in this family, and to identify by name 

 the species which I then indicated. 



Pentremite. 



Column cylindrical, perforated; segments articulating by ra- 

 diated surfaces, with cylindrical side arms at irregular inter- 

 vals : pelvis of three unequal pieces, two pentagonal and one 

 tetragonal : scapulce large, very profoundly emarginate for the 

 reception of the tips of the radiating ambulacrae, obliquely trun- 

 cated at the extremities on each side, for the reception of one side 

 of a subrhomboidal plate or interscapular : ambulacrce five, radi- 

 ating from the summit and terminating at the tips of the emargi- 

 nations of the scapulae ; each with a longitudinal, indented line, 

 and numerous transverse stria; which terminate in a marginal 

 series of pores, for the transmission of respiratory tubes : summit 

 with five rounded openings (ovaries) and an angulated central 

 one (mouth and anus.) 



This singular genus is so remotely allied to any other hitherto 

 discovered, that I do not think it can with propriety, be referred 

 to any family yet instituted. By its columnar support it is re- 

 lated to the family Crinoidea ; but the total absence of arms and 

 hands excludes it from that very natural group. The superior 

 termination, in which the ambulacrae, the rou»ded openings, and 

 the central angulated one, are situated, has some affinity to the 

 family Echinidea, but the columnar support shows that it cannot 

 be arranged there. 



Having thus on its inferior portion a resemblance to the Cri- 

 noidea, and on its superior surface a decided analogy to the 

 Ecliinidea, I think it may with propriety form an intermediate 

 family, under the following name and characters. 



Family^ Blastoidea. 



Column composed of numerous articulating segments, sup- 

 porting at its summit a number of plates, so united as to form a 

 calyciform body containing the viscera ; arms none ; branchiae 

 arranged in ambulacra?. 



