186 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



pore marginal; ambulacral furrows of inferior surface straight and simple. The largest specimens have a diameter of 1 J 

 inches, though the usual size is three-fourths of an inch. The disk is thin and flattened but shows a decided tendency 

 to form elevated stars on the upper surface. 



The writer's study of the specimens from the Button beds already referred to suggests a few 

 comments in connection with this description. The size of the specimens studied ranged from 8 

 to 15 millimeters in diameter. The marginal outline was usually circular, but sometimes longi- 

 tudinally oval. The marginal notches are often hardly discernible. The petals extend from 

 half to two-thirds the way to the margin. In some specimens the petals were practically flush 

 with the surface and in some were slightly tumid. In some the poriferous zones of all the petals 

 diverge continuously and are wide open at the ends, though the odd petal is somewhat more 

 widely open than the rest; in others those of all but the odd petal are partly closed, as in the 

 form figured by Anderson. In the form figured by Arnold (which has been examined by the 

 writer) the poriferous zones of all but the odd petal diverge for about half their length, then con- 

 verge to a less degree so that at their ends they are only slightly nearer together than 

 midway, those of the odd petal diverging continuously to their ends, where they are far apart, 

 the inner lines of pores forming a well-defined V. In view of the variations indicated it 

 seems probable that among the small echinoids of the Button beds there are several forms, 

 possibly distinct species, which closely resemble each other in general appearance, while differing 

 in details. The lines between these forms can only be drawn by one who has access to the type 

 and to an extensive series of good specimens. However, the writer is of the opinion that, in view 

 of Anderson's significant remark that the test "shows a decided tendency to form elevated stars 

 on the upper surface, " the small button like forms with shghtly tumid petals are most typical of 

 the species S. merriarni. Some of the larger specimens assigned to S. merriami — such as the one 

 figured by Arnold — strongly resemble Scutella fairhanJcsi and, with further collecting and com- 

 parative study with the types of the forms involved in hand, may prove to be young specimens 

 of that species. Aside from its smaller size, the only important apparent difference between 

 Arnold's figured form and S. fairhanksi is that the periproct is exactly marginal, visible from 

 above and below; but it may be found that S. fairhanksi, which is somewhat variable in regard to 

 this feature, may vary enough to include forms with a marginal periproct. 



There is some doubt in regard to the generic position of the present species. There seems to 

 be no good ground for placing it in the genus Astrodapsis, as it lacks the depressed apical system 

 and deeply impressed interambulacral areas characteristic of that genus. Anderson says that 

 the ambrdacral furrows are straight and simple, which, if true, would suggest placing it in the 

 genus Sismondia, but on the other hand in the figure of the under surface given by Anderson the 

 furrows appear to be simple and straight for about two-thirds of the way to the margin and then 

 bifurcate symmetrically, which fact points toward the genus Scutella. It is not improbable that 

 both genera may be represented. The ambulacral furrows are not discernible upon the speci- 

 mens studied by the writer, and the form is therefore, for the present, placed doubtfully in the 

 genus Scutella. 



Localities. — Tar Springs, Ivrej^ehhagen's and Temblor, Mount Diablo Range, California 

 (F. W. Anderson) ; Garza Creek gorge in Reef Ridge, Canoas Canyon, near Hugo Kreyenhagen's 

 place, and 8J miles north of Coalinga, all in the Coalinga district, California (Arnold) ; Wagon- 

 wheel Mountain, Devils Den district, Kern County, Cal. (Arnold). 



Geologic horizon. — Vaqueros formation, lower Miocene. Occurs in the Button beds, which 

 are near the middle of the formation. 



Collections. — TJ. S. National Museum (165584, B; 165716, A); California Academy of 

 Sciences; F. M. Anderson. 



Scutella norrisi Pack. 

 Plate LXXXV, figure 9. 



Scutella (?) norrisi Pack, 1909, Univ. California Dept. Geology Bull., vol. 5, No. 18, pp. 277-278, PI. XXIII, fig. 3. 

 Echinarachnius norrisi Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 703. 



Description. — Since no opportunity has been had of studying any specimen of this species 

 the description of Pack is given verbatim: 



