Manual of the Paleontology of the Cincinnati Group. 



125 



Dysiactophycus mamillanum Miller and Dyer (Contri. to Pal. 

 No. 2, July, 1878, p. 2), is a name given to what was supposed to be 

 a sea-weed. It was described as mammiform or depressed conical, 

 from eight to twelve inches in diameter and from one and one-half to 

 four inches in height in the center. This " frond" was marked with 

 concentric rings, twelve to eighteen in an inch. It presents no other 

 characters, and it most likely represents an impressiom made by the 

 epithecal membrane of the base of a large species of Monticulipora. 



ECHINO DERM ATA. 



This sub-kingdom includes the well-known sea-urchins, sea- 

 cucumbers, sea-lilies, star fishes, etc. It contains a vast number of 

 living genera and species, and was well developed in some of its 

 classes far back in Paleozoic time. Its features are given by Dr. 

 Nicholson as follows : * 



" Simple marine organisms, which are mostly bilaterally symmet- 

 rical when young, but which in the adult condition have this bilateral 

 symmetry more or less extensively masked by a radial (usually pen- 

 tamerous) arrangement of their parts. An alimentary canal is present 

 with or without a distinct anus, separate from the proper body cavity. 

 A system of water vessels often communicating directly with the 

 exterior, and generally connected with protrusible tubes (feet) is pres- 

 ent. The nervous system is radiate, consisting of an oesophageal ring, 

 and radiating branches. The integument is characteristically hard- 

 ened by the deposition in it of carbonate of lime in the form of plates, 

 granules, or spicules." 



The sub-kingdom has been divided into two great divisions based 

 on the absence or presence of a stalk. To the former belong the 

 sea-urchins, the star-fishes, etc., and to the latter the crinoids. There is 

 a further division into classes, and then into orders and families. In 

 the present instance we shall disregard the two latter, inasmuch as it 

 frequently occurs that single genera give their names to families ; and 

 the number of genera is not sufficient to justify in this place so minute 

 a subdivision. The following classes are those found in the Cincinnati 

 Group. 



Man. of Palteont, vol. i., 1889, p. 361. 



