126 



Cincinnati Society of Natural Hisiory. 



Division A. — Echinozoa. * 



ClaSS I. ASTEROIDEA. 



Here belong the star-fishes, whose characters may be given as 

 follows : 



Body star-shaped or pentagonal, consisting of a central disk, 

 surrounded by five or more lobes or rays which radiate from the body, 

 are hollow and contain prolongations of the viscera ; integument 

 coriaceous and strengthened by irregular calcareous plates, or studded 

 with spines ; dental apparatus none ; mouth inferior and central ; 

 anus absent, or, if present, dorsal; ambulacral tube-feet protruded 

 from grooves on the under surface of the rays.f 



SYNOPSIS OF GENERA. 



1. — paLjEaster Hall. Disc present : ambulacral grooves deep, 

 either wide or narrow; oval plates five or ten; two rows of plates on 

 each side of groove, one adambulacral and one marginal row ; three 

 Or more rows above. 



2. — petraster Billings. Disc present : ambularcal groove narrow; 

 an incomplete series of plates between the adambulacral and marginal 

 plates. 



3. — palasterina McCoy. Disc present: ambulacral grooves 

 shallow ; oral plates ten ; marginal plates lacking, and only one row of 

 adambulacral plates. 



4. — stenaster Billings. Disc absent : ambulacral grooves shal- 

 low : oral plates ten ; adambulacral plates in one row, the marginal 

 plates absent. 



Genus 1. — PAL^EASTER Hall, 1852. 



Body stellate ; rays five, occasionally seven, spinous, composed 

 of five or more series of plates, generally two ambulacral, two adam- 

 bulacral (one on each side of the ambulacral groove), and two 



* Forms without a stalk. 



t Nicholson, Ibid. pp. 391-392. 



