126 



ing through the auxiliary side arms, which vessel was perhaps surrounded hy a 

 cuticle possessing the qualities of a nerve and muscle ; as appears very pro- 

 bab le in an animal where the nerves must have been so minutely distributed. 



On examination of the conformation of the analogous parts in. the Stelleridae,. 

 it is at once proved, 



That in the genera Ophiura?* Asteria, andEuryale, the ossicula forming the 

 arms proceed from an ossicular arrangement surrounding the mouth, whereas 

 in the Crinoidea the system of joints supporting the arm proceed from the base 

 of the cup containing the intestines, and are only loosely connected with the 

 muscle surrounding the mouth, by the plated integument covering that cup. 



In the three genera mentioned, the mouth is pentagonal, and provided with- 

 teeth, of which there are no traces in the Crinoidea. 



The following characters appear distinctive between the three above stated 

 genera of the Stelleridae, but still not such as to approximate any of them parti*- 

 cularly to the Criooidea : 



In the genus Ophiura, the abdominal cavity extends beyond the mouth in 

 a subglobose manner. 



In the Asteria, the abdominal cavity extends laterally over the ossicular 

 arrangement of the arms to admit ten coeca. 



In the Euryale, the protruding semiglobular abdominal cavity is formed by 

 ten plates, each two serving as a stay to an arm ; thus if the arms were removed, 

 these animals would exhibit by this arrangement of their plates in ten divisions, 

 and the teeth, a transition to the Echini. 



In the Ophiura; ? Euryale, and Asteria3, there exists no perforation in the 

 arm joints, hence the vessel passing through it in the Crinoidea is omitted 

 or differently placed. 



The inner lateral angles of the arms of the Asterire being provided with 



here add a mark of interrogation, not having had opportunity to examine Ophiura 

 sufficiently in its anatomical details, and judging therefore from delineation only. 



