CKETACEOUS ECHINODEKMATA. 97 



Dimensions. — Length 70 (?) millimeters; width 59 millimeters; height 41 millimeters. 



Description. — This large species is represented by a single specimen. The test is cordiform 

 in ambital outline and elevated. The upper surface is much inflated, sloping rapidly to the sides 

 and toward the posterior margin, which is much depressed. The ambulacra are deeply de- 

 pressed, in broad grooves which distinctly affect the ambital outline. The interambulacra form 

 projecting ridges, the posterior interambulacrum producing a sharp crest. The apical system 

 is situated in a pronounced apex anteriorly. The peristome is located in a well-marked depres- 

 sion near the anterior margin. 



Locality. — Sage Creek, S. Dak. 



Geologic horizon. — Pierre shale of Montana group, Upper Cretaceous. 



Collection. — Peabody Museum, Yale University (1863). 



Hemiaster lactjnosus Slocum. 



Plate L, figures 3a-d; Plate LI, figures la-i. 



Hemiaster lacunosus Slocum, 1909, Field Mus. Nat. Hist. Pub. 134, Geol. ser., vol. 4, No. 1, pp. 10, 11, PI. II, figs. 1-7. 



Determinative characters. — Test small, indistinctly cordate, upper surface slightly convex, 

 elevated posteriorly; sides inflated; lower surface nearly flat. Ambulacra narrow, poriferous 

 zones not deeply depressed the posterolateral pair being quite short. Peripetalous fasciole 

 distinct. Peristome large, near anterior margin. Periproct high on posterior truncated surface. 



Dimensions. — Length 17.8 to 23.4 millimeters; width 16.3 to 23.6 millimeters; height 11.8 

 to 17 millimeters. 



Description. — Slocum says: 



Test small, indistinctly cordate, ventral surface moderately convex, dorsal surface convex, strongly elevated in the 

 posterior interambulaeral area and gradually sloping with an indistinct anterior sulcus; anterior and lateral borders in- 

 flated, posterior margin truncated. Ambulacral areas petaloid, with straight petals situated in depressions of the surface, 

 the anterolateral pair nearly twice as long as the posterolateral pair; poriferous zones of the paired petals wide, pores 

 transversely elongate and situated far apart. Anterior petal longer but narrower than the others and situated in a 

 deep depression which grades into an indistinct anterior sulcus; poriferous zones of this petal narrow and far apart; 

 pores small, round, and separated by a tubercle. Interambulaeral areas broad and composed of large plates. Surface 

 of the test covered with a multitude of small tubercles with sunken areoles that increase in size toward the peristome. 

 The tubercles have perforated mamelons and crenulated bosses, the interspaces being filled with microscopic granula- 

 tions. Peripetalous fasciole wide and distinct, moderately bent inward between the petaloid areas except the two 

 posterior ones. Apical disk sunken, small, and situated somewhat posterior to the center of the dorsal surface, the four 

 genital plates distinctly perforated and separated by five small radial plates. Right anterior genital plate large, convex 

 and forming the madreporite. Peristome transversely arched, bilabiate, with prominent labrum. Periproct about 

 the size of the peristome, elongated vertically and situated near the top of the posterior truncation. 



Related forms. — H. lacunosus resembles H. parastatusvn general form and proportions, but is distinguished from that 

 species by its smaller size and by the sunken areoles of the tubercles. Moreover, the posterior interambulaeral area is 

 rounded, while in H. parastatus it is in the form of a ridge. H. lacunosus is similar to H. Stella in size, but differs from 

 it in the shape of the fasciole, the sunken areoles and the form of the anterior margin. It resembles H. dalli in having 

 sunken areoles, but in general form these two species are quite dissimilar. The specific name adopted refers to the 

 sunken areoles by which the species is distinguished. 



Locality. — Pontotoc and Houston, Miss. 



Geologic horizon. — Ripley formation, Upper Cretaceous. 



Collections.— U. S. National Museum (31204); Field Museum (P 10342). 



Hemiaster kixmmeli Clark. 



Plate LII, figures la-c. 



Tlemmster kiimmeli Clark, 1907, in Weller, Cretaceous paleontology of New Jersey: Geol. Survey New Jersey, pp. 

 303-304, PL XVII, figs. 1-3. 



Determinative characters. — Test cordate, slightly elevated. Upper surface nearly flat, with 

 weakly depressed petaloidal areas; the lower surface flat. Peristome with distinct overhanging 

 lip. 



Dimensions. — Length 30 to 55 millimeters; width 30 to 40 millimeters; height about 20 

 millimeters. 



