SYSTEMATIC PART. 153 



the ventral sac, was incapable of holding the visceral mass without incorpor- 

 ating the lower brachials. As such the Pentacrinidas may represent the last 

 survivors of an exhausted type, or they are the progenitors of a new group. 



After eliminating from the Articulata the Encrinidge and Pentacrinidse; 

 and all Crinoids in which the top stem joint is the youngest joint of the stem, 

 we have a well-defined group ; but it may be asked whether the name 

 Articulata can be retained for a group thus restricted and redefined. The 

 name is most appropriate, and as the group is based largely on the character 

 of Miiller, we think it is just to the author to adopt his name. In case, how- 

 ever, other writers conclude that this course is inadmissible, we propose the 

 name " Articulosa " to take the place of Articulata, to meet the contingency. 



That our primary divisions are natural groups is further confirmed by the 

 orientation of the base, which, when the proximal ring of the base is un- 

 equally tripartite, varies among the different groups. Comparing the 

 base to the dial of a clock with the anal side at 12, it may be said that in 

 the Impinnata the smaller infrabasal points to 2 o'clock; in the dicyclic 

 Fistulata,^ so far as observed, and in the Antedon larva, according to Bury, 

 to 6 o'clock; and that the small basal in monocyclic Crinoids generally 

 points to 7 o'clock, contrary to all Blastoids, in which it points to 5 o'clock. 

 We have no explanation of these facts to ofPer, but they doubtless have an 

 important bearing upon the derivation of the groups. 



It is now well established that the value of a character for classificatory 

 purposes is not always in proportion to its physiological importance; but 

 depends more on its constancy throughout groups, and its correlation with 

 other characters. The characters of any group are not fixed and rigid, but 

 w^e must always be prepared to find as to one or more of them variations or 

 departures from the typical form, indicating a transition toward, or con- 

 nection with, some other group through that particular feature. We cannot 

 expect absolute persistence of any one character, whether specific, generic, 

 or ordinal, and the larger our collections the less persistent and fixed will we 

 find the separate characters. But if we are reasonably happy in our identi- 

 fications, we may expect to find greater reliance to be put upon the corre- 

 lation of characters, so that while one or more of them will show a tendency 

 to departure, the sum of all will exhibit a predominance which will hold the 

 form in question within the given group. There is no hard and fast rule by 

 which it may be determined that a certain character is of "family" or 

 "generic" importance. It may be the one or the other according to cir- 



* This does not hold good for the Fistulata since Mr. Bather — Crinoidea of Gotland, Vol. I. p. 152 — 

 has found that the position of the small infrabasal is not constant in the Gotland species of 



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