32 THE MESOZOIC ECHINODERM^TA OF UNITED STATES, {bull. 97. 



giou and of a limited horizon. The .sandstone is marked by the hiyers 

 in which they are found by ripple or wave marks, having a width of 

 about 3 inches, and indicates a near proximity to a shore line over the 

 area where they were obtained, and that the individuals are probably 

 stranded specimens. A single very imperfect impression of a lamelli- 

 brauchiate shell is present on the same fragments of rock, but too 

 imperfect for determination." 



Related forms. — This very doubtful species scarcely admits of com- 

 parison with other forms. There is nothing hitherto reported from 

 American strata that can be closely associated with it. 



Locality and geological horizon. — This form is reported by Whitffeld 

 as occurring "in red sandstones of Jurassic age, 70 feet above the red 

 beds, on the east side of Spearflsh creek, near its junction with the 

 Kedwater, Black Hills, Dakota." 



Collection. — U. S. National Museum. 



GONIASTER Agassiz. 



GONIASTER MAMMILLATA Gabb. 



Plate V, Figs. la-h. 



Goniaster mammiUata Gabb, 1876. Philadelphia Acad. Nat. Sci. Proc, vol. 28, pp. 

 178, 179, Figs. 2, 2a, 2b. 



Determinative characters. — Body pentagonal, provided with a dorsal 

 and a ventral row of marginal plates that are narrower than high, and 

 distinctly tumid on their outer surfaces. Only detached marginal 

 plates preserved. 



Description. — Gabb mentions the discovery of about thirty detached 

 marginal plates of this species. They differ widely in shape by reason 

 of their position upon the margin, but among those examined the ma- 

 jority are higher than wide, and swollen on the outer surfaces. Certain 

 of the plates show marked protuberances upon the general level of the 

 plate (PI. v, Figs, la, lb). The surface of the plates is punctate, the 

 small depressions being arranged in rows that cross one another at 

 right angles (PI. v, Fig. Ih). 



Belated forms. — There are no American forms similar to this species 

 with which it may be confounded, while the absence of all knowledge 

 of the characters outside of a few marginal plates renders wide com- 

 parisons impossible. 



Locality and geological horizon. — Yellow limestone of. the middle 

 naarl bed of the Cretaceous from Vincentown, New Jersey. 



Collections. — Philadelphia Academy of Natural Sciences ; Johns Hop- 

 kins University. 



