176 



OOLITIC ECHINODEUMATA. 



Gems 10. — Magnotia, Michelin (Vol. I, p. 190). 



Test thin, small, inflated, with a concave base. Ambulacral areas narrow 

 and straight. Interambulacral areas marked by a deep median depression, and bearing 

 many small, equal-sized, imperforate, and uncrenulated tubercles. Poriferous zones 

 narrow; pores unigeminal. Genus found in the Oolitic strata. One British Oolitic 

 species (Vol. I, p. 191). 



Genus 11. — Polyctphus, Agassiz (Vol. I, p. 196). 



Test thin, small, hemispherical. Ambulacral areas narrow and straight. Interambu- 

 lacral areas wide, with a slight median depression. Both the ambulacral and the inter- 

 ambulacral areas are covered with numerous small equal-sized, regularly-arranged, imper- 

 forate tubercles, which are much larger on the under side than on the upper surface. 

 Poriferous zones wide and depressed. Pores in triple oblique pairs, which become most 

 numerous near the peristome. Oral opening wide. Peristome pentagonal, slightly 

 notched, and marked by unequal lobes. Genus found in the Oolitic strata. Two 

 British Oolitic species (Vol. 1, pp. 197—199). 



Genus 12. — Stomechinus, Besor (Vol. I, p. 203). 



Test thin, of moderate size, globular, conoidal, more or less depressed. Ambulacral 

 areas narrow, one third the width of the ambulacral, bearing two marginal rows of 

 numerous small tubercles, and sometimes two additional rows of a smaller size. Inter- 

 ambulacral areas wide, bearing two rows of larger tubercles and several rows of smaller 

 tubercles. Miliary zones sometimes broad and granular, sometimes narrow and naked. 

 Poriferous zones moderately wide ; pores arranged in triple oblique rows. Mouth 

 opening large. Peristome subpentagonal, deeply notched, and unequally lobed. Spines 

 short, stout, and bluntly pointed. Genus found in the Oolitic strata. Six British Oolitic 

 species (Vol. 1, pp. 204—217). 



Family V.— SALENIADiE, Wrigld (Vol. I, p. 226). 



Test thin, small, spheroidal or depressed. Ambulacral areas always narrow, straight, 

 or flexuous, with two rows of small tubercles, which alternate with each other on the 

 margins of the areas. Interambulacral areas wide, with two rows of large primary 

 tubercles, perforated or imperforated, with bosses having crenulated summits. Poriferous 

 zones narrow ; pores unigeminal, except near the peristome, where they are obliquely 



