90 MESOZOIC ECHlNODERMATA OF THE UNITED STATES. [bull. 97. 



Hemiaster californicus Clark. ^ 



Plate XLix, Figs. la-c. 



Hemiaster californicus Clark, 1891. .Johus Hopkins University Circulars, No. 87, p. 77. 



Determinative characters. — Test small, subquadrate, depressed; up- 

 per surface flat, with shallow anterior sulcus, sloi^iug sides, and low 

 truncated ijosterior margin; lower surface flat. Ambulacra depressed, 

 in shallow furrows. Apical disk small, posterior to center. Mouth 

 opening transversely oval near anterior margin. Anal opening situ- 

 ated on the low truncated surface of the posterior margin. 



Dimensions. — Length, 1 inch; width, 1 inch; height, J inch. 



Description. — This form, the single representative of the Echinoder- 

 mata thus far obtained from the Cretaceous deposits of California, has 

 the details of its structure poorly preserved in the specimens examined, 

 although it belongs, beyond much doubt, to the genus Hemiaster. 

 The test is small, much depressed, and subquadrate in ambital outline. 

 It is broader anteriorly, with a feeble groove in the center of the ante- 

 rior margin. The posterior portion of the test is but slightly more 

 elevated than the anterior, and the truncated margin is low and narrow. 

 The base is flat, wdth the exception of the peristomial depression. 



The ambulacral areas are but slightly depressed in the petaloidal 

 portions. The poriferous zones are broad, and the oval pores are united 

 by shallow furrows (PI. xlix. Fig. la). 



The apical disk is small and situated slightly forw ard of the center. 



The mouth opening is transversely oval and situated near the ante- 

 rior margin (PI. xlix, Fig. Ih). The anal opening is small, oval, and 

 situated on the low, truncated surface of the po sterior border. 



Related forms. — On account of its shallow ambulacral furrows, Hemi- 

 aster californicus may be compared to H. Hamphreysanus , but is readily 

 separated from it by means of its more central apical disk and its 

 depressed form. It is a very unique species. 



Locality and geological horizon. — H. californicus is from Redding, 

 Shasta county, California, in deposits that have been referred to the 

 Chico group (ujjper Cretaceous). 



Collection. — U. S. National Museum. 



Hemiaster Calvini Clark. 

 Plate XLIX, Figs. 2a-i. 



Determinative characters. — Test oval, cordate, inflated; upper sur- 

 face elevated ; lower surface flat; [)osterior margin obliquely truncated. 

 Ambulacra moderately depressed on the upper surface. Mouth open- 

 ing transversely oval. Anal opening oval, high on truncated iiosterior 

 border. 



Dimensions. — Length, 1^ inches; width, 1^ inches; height, ^ inch. 



Description. — This species has an elevated test that is oval, cordate, 



