May, 1909. New Echinoids — Slocom. 9 



Family SPATANGID^). 

 Genus HEMIASTER Desor 1847. 



Urchins with a short, elevated, oval or cordiform test. Apical 

 system in general excentral and posterior. Ambulacral areas peta- 

 loid, unequal in length, and lodged in depressions of the dorsal surface; 

 poriferous zones large and equal in the same ambulacral area, pores 

 elongated and placed close together. Anterior area lodged in a long 

 shallow sulcus; poriferous zones very narrow and composed of small 

 round pores sparsely disposed in oblique, widely separate, simple 

 pairs. Fasciole single, peripetalous, and circumscribing the ambul- 

 acral areas. Apical disc small and compact, four perforated genital 

 plates, and five very small radial plates. Peristome bilabiate, 

 very excentral, opening at the anterior fourth part of the base. Peri- 

 proct opening high up on the posterior border, which is in general 

 flat, and obliquely truncated. 



Hemiaster differs from Micraster in having a single peripetalous 

 fasciole and no anal fasciole; the test is likewise in general shorter, 

 more inflated, and the posterior pair of ambulacral areas are much 

 shorter than the anterior pair. Hemiaster differs from Linthia in 

 having only a peripetalous fasciole, the latter having both peripetalous 

 and lateral fascioles. 



Range Cretaceous to Recent. 



Hemiaster parastatus (Morton). 



1830. Spatangus sp. Mort., Am. Jour. Sci., 1st ser., Vol. 17, p. 286. 

 1830. S. cor-marinum (?) Mort., Am. Jour. Sci., 1st ser., Vol. 18, 



p. 250, pi. 3, fig. 10. 

 1830. 5. cor-marinum (?) Mort., Jour, Acad. Nat. Sci. Phil., 1st 



ser., Vol. 6, p. 199. 



1833. S. parastatus Mort., Am. Jour. Sci., 1st ser., Vol. 23, p. 294. 



1834. 5. parastatus Mort,. Synop. Org. Rem. Cret. Gr. U. S., p. 77, 

 pi. 3, fig. 21. 



1853. Hemiaster parastatus Marcou, Explan. Text to Geol. Map. 



U. S., and Brit. Prov. N. A., p. 47, pi. 7, fig. 8. 

 1855. H. parastatus d'Orb., Pal. France, Terr. Cret., Vol. 6, p. 265, 



pi. 894, fig. 4. 

 1864. H. (?) parastatus Meek, Check List Inv. Foss. N. A., Cret. 



and Jur., p. 3. 

 1891. H. parastatus Clark, Johns Hopkins Univ. Circ, Vol. 10, 



No. 87, p. 77. 



