Bkede.] 



( 'arboniferons Invertebrates. 



27 



Resting on the radials are the arm plates. The arms are 

 five or ten in number. They are composed of short plates laid 

 one on top of another, and 

 capable of motion. The A 3 --* S-- ^ 

 inner side of the arms has I// 

 usually a groove, along 

 each side of which is a 

 row of smaller armlets or 

 pinnules. These grooves 

 connect at the base of the 

 arms with what are called 

 the ambulacral areas, 

 which in turn connect 

 with the mouth, where 

 food particles which are 

 carried in the water are 

 selected out. 



The ventral side or top 

 of the animal is often pro- 

 duced into a ventral sac, 

 or anal tube, as it is some- 

 times called. The anal 



opening is either on top or in one side of this sac. The mouth 

 is almost always centrally located. The crinoids are more closely 

 related to the starfish and the sea-urchins or sea-cookies than 

 to any other animals. 



In the accompanying figures the various parts of the crinoid 

 are shown and designated. 



SCAPHIOCRINUS. 



Hall, Geol. Surv. Iowa, p. 550, (1858). 



Scaphiocrinus? washburni. Plate VI, figs. 2, 2a. 



Fig. 2. Diagrammatic view of a crinoid with the plates 

 separated, showing their relative form and posi- 

 tions. The black spot in the center is the hole in 

 the base of the calyx that communicates with the 

 stem. lb, infrabasals: b, basals ; r, radials; br, 

 costals; «, anal. The remainder are arm plates. 



Scaphioerinust washburni Beede,Kans. Univ. Quart., i, p. 21, pi. v 



2a, Q899). 



ff. 2, 



Calyx broadly obconical, somewhat wider than high, rather 

 stout, and smooth. Infrabasals rather largo, bent upward ai 

 outer end, exterior outline pentagonal, plainly visible in the 

 side view of the calyx, well defined. Column large, circular, 



