42 MESOZOIC AND CENOZOIC ECHIN ODERMATA OP THE UNITED STATES. 



The specimen also more or less closely resembles, in the characters preserved, some of the 

 recent species of Gnathaster, a genus also belonging to the family Pentagonasteridee, in which 

 the interradial arcs are in many specimens much deeper than in Pentagonaster, the proportion 

 of the minor to the major radii in G. elongatus Sladen x being 1 to 3.5. Gnathaster, however, is 

 customarily characterized by the presence of an odd interradial marginal plate, a character not 

 clearly shown in the fossil specimen. In one of the interradia such a plate seems to be present, 

 but in the others not. For the present, therefore, the specimen may be referred to the genus 

 Pentagonaster (Weller) . 



Locality.— SE. I sec. 16, T. 32 N., K. 99 W., near Lander, Wyo. 



Geologic horizon. — Montana group, Upper Cretaceous. 



Collection. — Walker Museum, Chicago. 



Family ATHENEIDJE. 



Genus GONTASTER Agassiz (em. Per.). 



GONIASTER MAMMILLATA Gabb. 



Plate VIII, figures la-h. 



Goniaster mammillata Gabb, 1876, Acad. Nat. Sci. Philadelphia Proc, vol. 28, pp. 178, 179, figs. 2, 2a, 2b. 

 Goniaster mammillata Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Goniaster mammillata Clark, 1893, U. S. Geol. Survey Bull. 97, p. 32, PI. V, figs. la-h. 

 Goniaster mammillata Johnson, 1905, Acad. Nat. Sci. Philadelphia Proc, vol. 57, p. 6. 



Goniaster mammillata Weller. 1907. Cretaceous paleontology of New Jersey: Geol. Survey New Jersey, pp. 277-278, 

 PI. VI, figs. 10-17. 



Determinative characters. — Body pentagonal, provided with a dorsal and a central row of 

 marginal plates that are narrower than high, and distinctly tumid on their outer surfaces. Only 

 detached marginal plates preserved. 



Dimensions. — Plates: Height 3 to 8 millimeters; thickness 2.5 millimeters. 



Description. — Gabb mentions the discovery of about thirty detached marginal plates of 

 this species. Many more have been found by the author. They differ widely in shape from 

 their position on the margin, but among those examined the majority are higher than wide and 

 are swollen on the outer surfaces. Certain of the plates show marked protuberances upon the 

 general level of the plate. The surface of the plates is punctate, the small depressions being 

 arranged in rows that cross one another at right angles. 



Related forms. — No American forms are similar enough to this species to be confounded with 

 it. Lack of knowledge of all characters except those of a few marginal plates renders wide 

 comparisons impossible. 



Locality. — Vincentown, N. J. 



Geologic horizon. — Vincentown sand of Rancocas group, Upper Cretaceous. 



Collections.— Academy of Natural Sciences of Philadelphia (1457); Johns Hopkins 

 University. 



Family PENTACEROTIDJE. 



Genus PENTACEROS Linck. 

 Pentaceros aspertjltjs Clark. 

 Plate VIII, figures 2a-b. 

 Pentaceros asperulus Clark, 1907 ; in Weller, Cretaceous paleontology of New Jersey : Geol. Survey New Jersey, pp. 278- 

 279, PI. VI, figs. 18, 19. 

 Determinative characters. — Body pentagonal with long, narrow arms; covered with irregu- 

 larly shaped plates that touch intermittently at their margins, the surface uneven and bearing 

 spines. Detached body plates alone found. 



i Idem, p. 288, PI. XLVIII, figs. 1, 2. 



