JUN 



25 1900 



THE DEVELOPMENT OF AGARICOCRINUS.* 

 Mary Klem. 



In recent works on the Crinoideae of North America, we 

 find the writers relying upon the variations in the proportions 

 of the interbrachial plates, and upon the form and size of the 

 costals and distichals as the best distinctive characters for 

 specific separation. The number and distribution of the arms, 

 the form of the anal area, and the condition of the oral 

 plates, are also important features. 



I have examined a large and excellent collection of Agari- 

 cocrini, numbering over one hundred well preserved specimens, 

 gathered at Moore's Mill on the Fox River, in Clark Countv, 

 Missouri, from the Keokuk formation. The diversity of their 

 general form and the various stages of the development of 

 the plates, comprising the calyx, would tend to support the 

 above statements ; but, on closer investigation, I became fully 

 convinced that the specimens before me belong to but one 

 species. The fact that these fossils were found within the 

 small radius of one-eighth of a mile strengthens the stand I 

 take on this question. I consider the prevailing differences in 

 the plates the result of abnormal development, otherwise I 

 would have one hundred species of the same genus from one 

 locality, which is an utter impossibility. 



On the ventral side of any one of these specimens, there 

 are invariably six prominent plates, each of which is sur- 

 rounded by a more or less perfect ring of smaller pieces. In 

 all the specimens that have come under my observation, and 

 in the drawings I have examined, I have found these essential 

 points. This fact led me to the following conclusions con- 

 cerning the development of this genus. 



According to my conception of their development, the first 

 plates to be formed were the orals, six in number. These 



* Presented by title to The Academy of Science of St. Louis, May 7, 

 1900. Presented to the Faculty of Washington University as a thesis for the 

 Degree of Bachelor of Arts, June, 1900. 



(167) 



