Klem — Tlie Development of Agaricocrinus. 169 



the orals and some of the plates composing the ring, as shown 

 in Figs. 5, 18, 22 and 25. These may have been formed 

 while the animal was sick or in a poor locality. Upon a 

 return to more favorable conditions, the ring of larger 

 plates was deposited. The isolation of the orals by these 

 supplementary pieces cannot very well be regarded as of 

 specific importance, as there is no regularity in their occur- 

 rence. 



Because of the great variety in the shape, size, and number 

 of the pieces, I think the intervening spaces were filled out 

 as the necessary material could be produced. The sole pur- 

 pose of these plates seems to be to fill out space, no one know- 

 ing any functions which they might have had. Since their 

 only object is to connect the different parts, it is very reason- 

 able to suppose that they made their appearance at a later 

 period than the orals and the basals, which appeared simul- 

 taneously. Here, again, it is impossible to find any two 

 specimens in which the spaces have been filled out in the same 

 manner. An examination of the drawings accompanying this 

 paper will show every possible combination, resulting from 

 the factors with which the animal had to contend. The 

 number of drawings could have been multiplied many times, 

 but I think those submitted are sufficient to show the chief 

 features in the development, and the departure in each case 

 from the regular pentamerous arrangement. 



This process of development necessarily affected the gen- 

 eral shape of the calyx, making it hemispherical as in A. 

 Americanus, pyramidal as in A. excavatus, conical as in A. 

 conicus, or inflated as in A. inflatus. In many cases the sym- 

 metry of the body was destroyed by the addition or the 

 removal of arms or plates . The size of the calyx is of little 

 value for classification, as it depends entirely upon the size 

 and number of the component plates. 



Examining the dorsal cup, I found a great similarity in the 

 general arrangement of the plates, but differences in the 

 number and in the size of the plates were as prevalent as on 

 the ventral side. The many variations in the structure have 

 been mistaken for specific differences, giving rise to useless 

 synonyms. 



