MORPHOLOGICAL PART. 135 



include both forms, its value as a full generic character might well be 

 doubted. It was probably this that led Meek and Worthen to establish 

 subgenera for these forms. We finally concluded to make them full genera, 

 finding considerable objection among naturalists to sabgeneric divisions. 

 Only in Platycrinus and Melocrinus were we obliged to retain both forms 

 under the same generic name, as we are unable to separate them. Their 

 tegmens are rarely preserved, and among the species of Platycrinus espe- 

 cially are found all possible gradations from a simple opening to a good 

 sized tube. 



As a rule, a tube occurs more frequently among species in which the 

 arms form a continuous series around the calyx ; while species in which they 

 are arranged in clusters often have a simple opening. Most of the latter 

 forms have a wide, more or less depressed space along the disk, between the 

 two posterior rays, for the foecal matter to pass out ; but when the tube is 

 long, and the arms in close contact all around, the excretions were dis- 

 charged above the arms. 



Occasionally, among species with a slender tube, we find specimens in 

 which during the life of the animal the tube was broken at the base, and 

 the fractured edges upon the disk were rounded off by calcareous growth, 

 so that it appears like a simple opening. From this we conclude that the 

 tube had no important bearing upon the general organization of the animal, 

 and that the Crinoid could live without it. This is also indicated by speci- 

 mens in which the anal tube was obstructed, and a new passage formed 

 at another place. Abnormal passages of this kind occur along the tube, 

 upon the disk, within the dorsal cup, and even within the basal ring. 

 They are more or less restricted to the posterior side, but are not neces- 

 sarily in a vertical line with the anus, as we formerly supposed. When 

 it occurs within the basal ring, the opening is located anteriorly, but 

 turns to the right whenever it enters the sides of the dorsal cup. It is 

 located posteriorly — or nearly so — close to the arm bases, but above the 

 calyx it may occur on any side of the tube. The Museum of Comparative 

 Zoology has a very interesting specimen of Batocrinus longirostris, in which 

 a new tube of the same size as the original one has been formed just 

 above the calyx. In this instance apparently the second tube also became 

 obstructed, and a third one was in process of formation. A similar case is 

 presented by our specimen of Batocrinus laura (Plate lY., Fig. 14). The 

 tube in the specimen of EidrocJiocrinus Ohristyi (Plate lY., Fig. 16) gives off 



