EXHIBIT AT PAN- AMERICAN EXPOSITION. 225 



forms without stems or anchoring structures. The latter are adapted to free loco- 

 liinti in either by swimming or by crawling about by the brachia. 

 24,887. Ordovician stems and stem ossicles. St. Paul, Minn. 

 L5,518. Stem of Glyptocrinus. Winding around foreign object. Upper 



( ►rdovician. 

 .'54,0!)1. Upper Silurian stem and stem ossicies. Dayton, Ohio. 

 26,4<>s. Myrtilloerinus butbosus. Middle Devonian. Stem ending in a four- 

 fluked grapnel. 

 34,086. Stem and ossicles of Platycrinus. Lower Carbonic. The spiral twist 

 of the flattened stem enables the animal to turn in any direction. 



34.092. Stem with cirri. Lower Carbonic. 



ROOTS. 



(See Plate 68.) 



The roots are distal branches of the stem, and, like it, are usually made up of per- 

 forated ossicles. In some forms the stem terminates in a disk-shaped or encrusting 

 nonsegmented root. 



34,089. Anomalocrinus incurvus. Growing upon a monticuliporoid bryozoan. 

 Upper Ordovician. 



34.093. Knot of Ectenocrinus(?). Upper Ordovician. 

 10,425. Eucalyptocrinus crassus. Upper Silurian. 

 34,088. Poteriocrinus spartarius. Lower Carbonic. 



Injuries. 



Crinoids are found which during life had lost a considerable portion of the brachia. 

 Such lost parts may be subsequently regrown and pass through the same growth 

 stages as the adult. 



The stems when fractured repair the broken place by profuse calcareous deposit, 

 as shown by the annexed specimens. 



( KINOID PARASITES. 



i See Plate 69.) 



Gastropods of the genera Cyclonema and Platyceras are found situated over the 

 anal region of many crinoids. In the Silurian and Devonian such occurrences are 

 rare and there do nut appear to have been permanent parasites. In the Lower Car- 

 boniferous, however, the form of the shell is considerably modified and perfectly 

 molded to the crinoid, proving that the Platyceras spent its life where found. Its 

 sustenance, therefore, must have been largely the effete matter of the crinoid. 



15,513. Glyptocrinus decadactylus. The parasite is Cyclonema bilix. Upper 

 Ordovician. 



26,465. Arthracantha punctobrachiata. The parasite is Platyceras dumosum 

 rarispinum? Middle Devonian. 



24,185. Platycrinus hemisphericus. Lower Carbonic. The parasite is Platy- 

 ceras uncum. 



CRINOIDAL, LIMESTONE. 



Limestones are found, many feet in thickness, almost entirely made up of the dis- 

 jointed skeletal parts of crinoids. Such limestones are usually of local occurrence, 

 but in the region of Iowa and .Missouri the Burlington crinoid limestone extends for 

 more than 300 miles. This is the most extensive crinoid bed, having furnished 

 between 300 and 400 species and many thousands of individuals. 



15518. Upper Ordovician crinoidal limestone, from Madison. 1ml. 

 34094. Lower Carbonic crinoidal limestone, from Burlington, Iowa. 



NAT MUS L901 15 



