1881.] ■ NATURAL SCIENCES OF PHILADELPHIA. 193 



contraction of the long solid tube of Acfinoo'inus, as has been 

 suggested by Austin, is wholl3' impossible. 



There has been considerable difference of opinion as to whether 

 species with a solid anal tube should be separated from those with 

 a simple opening. Cousidering the slight distinctious upon which 

 many of the genera have been founded, it would seem that the 

 tubular structure ought to be of sufficient importance to justify a 

 generic separation ; but when we consider that various generic 

 groups, after being carefully restricted with reference to all other 

 characters, include both forms, its value as a full generic character 

 must be somewhat doubtful. We once supposed that it might be 

 a sexual difference, but the specific relations of the forms thus 

 distinguished do not sustain that supposition. Both forms are 

 not found in all the groups, though they exist in many, and 

 throughout all divisions of this famil}'. In some cases generic 

 separations have been made upon this character, as for instance 

 Physetocrinus has been divided from Actinocrinus, Alloprosallo- 

 crinus from Agaricocrinus^ etc., while in other cases as Platy- 

 criniis^ GJy2:)tocrinus and Strotocinnus both forms have been 

 retained in the same genus. It must also be observed, in this 

 connection, that in some cases, especially species with a very 

 slender proboscis like Batocrinus rotundus^ we find occasionally 

 specimens in which the tube seems to have been accidentally 

 broken awaj^ during the life of the animal, and in which the 

 fractured edges of its base had become absorbed and rounded, 

 giving it the appearance of a naturalh^ simple oj>ening. That the 

 simple opening could have been produced in a like manner in 

 Strotocrinus and other genera, no one would for a moment suppose 

 after examining good specimens. 



The fact that the crinoid lived on without the tube, at least 

 proves that this structure had no important influence upon the 

 general organization of these animals. 



A tube is more freqiiently found in genera in which the arms 

 are arranged in a continuous series around the body, while in 

 species with a simple lateral opening the arms are arranged more 

 or less in clusters, leaving wide spaces between the ra3's. In the 

 former case, the long tube could discharge the excrements free 

 from the arms, and in the latter it was not needed as the refuse 

 matter could be easily discharged between the bases of the arm 

 clusters. In view of these facts, we think a subgeneric division 



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