MORPHOLOGICAL PART. 5 
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 subgenerie 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 Plutycrinus 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 
Zovlogy 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 IV., Fig. 14). The 
tube in the specimen of Lutrochocrinus Christyi (Plate IV., Fig. 16) gives off 
c 
