Klem — The Development of Agaricocrinus. 175 



have examined the specimen from which Shumard made his 

 description and am at a loss to see any difference. The 

 specimen, which is now in the collection of the Washington 

 University, was found at Button Mould Knob in Kentucky, 

 the same locality which Miller mentions for his specimen. 

 Because of the possession of one more arm Zeacrinus 

 bellulus is separated from Zeacrinus maniformis, which was 

 described by Hall in 1858* as having nine arms which he 

 distinctly states is probably accidental. f 



Besides the foregoing reasons for reducing the existing 

 number of species, the following characteristics will help to 

 prove my assertions : — 



(a) Concavity of the base. — Messrs. Wachsmuth and 

 Springer J state that " the Keokuk species without exception 

 are deeply concave, in the basal regions," but I have found 

 all possible gradations from an almost flat basal region to a 

 deeply concave disk. A. Whitfieldi is so deeply concave, 

 that when the body is placed upon a level surface, it rests 

 upon the first brachials. In A. tuberosus and A. Americanus 

 the concavity involves the entire radial series of the plates ; 

 in A. splendens it extends to the top, and in A. nodulosus to 

 the middle of the first distichals ; in A. Wortheni, to the sec- 

 ond costals ; in A. nodosus and A. conicus, to the first cos- 

 tals, and in A. crassus it is almost flat. The difference in 

 the concavity is such a gradual variation, that it is impossible 

 to state the extent of concavity permissible for a certain species. 



(b) Horizon and locality. — A great many of the species 

 recently described were collected at the same place and from 

 the same geological formation. From Charlestown, Indiana, 

 Miller alone described thirty-five new species of Dolatocrinus 



* Geol. Rep. Iowa. I 2 : 682. pi. 25. f. 8. 



t For further examples of abnormal development see Bull. 111. State 

 Mus. Nat. Hist. 3:19, 35,36,37,46; 5:39,53; 6:16; 7:6,8,19,21,22,25, 

 28, 29, 31, 40, 63, 67; 8: 6, 8, 9, 10. — Trans, and Proc. New Zealand Insti- 

 tute. 1894. 27 : 194-208. pi. X, XI, XII, and XIII (in part). — Quarterly 

 Journal Geological Society. 45 1 . No. 177: 149-171. pi. VI. (1889); 38. 

 (1882).— G. Boehm. Zeitschrift der Deutschen geologischen Gesellschaft 

 43 3 . Uber eine Anomalie im Kelche von Millericrinus mespeliformis.— 

 Quenstedt. Fetrefactenkunde Deutschlands. 4:328.— F. de Loriol. M4m- 

 oires de la Society Paleontologique Suisse. 4. 



X Revision Palaeocrinoidea. Part II. 109. 



