MIOCENE ECHINODERMATA. 179 



pointed, approximately equal in length to the width of the dorsal median platea. Under arm plates simple, breadth 

 about 1J length; lower arm plates deeply grooved in the median line. 



Disk pentagonal in outline, the arms passing out from the sides rather than from the angles, this being due to the 

 spreading of the disk upon compression by the containing fine clayey sediments; whole dorsal surface of d°isk covered 

 with overlapping scales, which, in the cast serving as the type, are minutely shallowly punctuate corresponding to 

 numerous microscopic protuberances in the original animal. Radial shields moderately large, of a short, pear-seed 

 shape, pointed within, outer edge sharply rounded, inner edges nearly straight and separated' by five prominently 

 overlapping scales (the continuation of the upper arm scales, but shorter than the latter) which narrow rapidly toward 

 the points of the shields. Between the radial shields of adjacent arms are about seven rows of small overlapping 

 plates, the middle row apparently much larger than the others. The specimen exhibiting the ventral side is 

 so much crushed that its characteristics are unrecognizable. Upper arm plates simple, small, breadth about 1$ 

 length, slightly narrowed within, broader without, straight front, back, and sides. Side plates small, triangular, 

 with sharp cornered, beveled edges. Under arm plates quite similar to upper, except deeply medially longitudinally 

 grooved. Spines at least four to a segment; about 1J times length of upper arm plates, rounded, sharp. 



Dimensions.— Specimen exhibiting dorsal surface: Diameter of disk 13 millimeters; arms at least 25 millimeters 

 long and probably several times this amount; width near disk 2 millimeters, upper arm plates 0.7 to 0.8 millimeter 

 long. 



Specimen exhibiting ventral surface: Diameter of disk 6.5 millimeters; arm at least 20 millimeters long and 

 probably at least twice this length judging by taper. 



Notes.— The two specimens upon which this species is founded are beautifully preserved molds, the larger one, 

 which is taken as the type, showing the dorsal surface, the smaller one the ventral. As would be expected, the surfaces 

 of the disks are considerably crushed and distorted, but enough characteristics are visible to admit of the above 

 specific description. The specimens have been compared with the recent alcoholics in the collection of the United 

 States National Museum, but no forms agreeing even remotely with the fossils were found. Both A. H. Clarke and 

 the writer are of the opinion that the fossils belong to the genus Amphiura, although, as might be expected in 

 molds, some of the diagnostic characters are lacking. The species is named in honor of the Santa Cruz quadrangle, 

 near which the types were obtained. 



Locality. — Hills immediately southeast of Scott Valley, 6 miles north-northeast of Santa 

 Cruz, Santa Cruz County, Cal. 



Geologic horizon. — Santa Margarita formation, middle or upper Miocene. 

 Collection. — Stanford University (1078); U. S. National Museum (165431). 



Class ECHINOIDEA. 



Subclass REGULARIA ENDOBRANCHIATA. 



Order CIBAROIDEA. 



Family CIDARIDJE. 



Genus CIDARIS Leake. 



Cidaeis thouarsii ( ?) Valenciennes. 



Cidaris thouarsii Valenciennes, 1846, Agassiz and Desor, Cat. raisonn^ des £chinodermes, Soc. nat. Ann., vol. 6, p. 326. 

 Cidaris sp. a Arnold, 1908, U. S. Nat. Mus. Proc, vol. 34, pp. 351, 359. 

 Cidaris sp. a Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 701. 



Description. — This species, which Arnold has referred to under the name of Cidaris sp. a, is 

 regarded by H. L. Clark as probably C. thouarsii. He says in a letter quoted by Arnold : 



The wax cast [Cidaris sp., a] is a spine of a true Cidaris and very much like many spines of some individuals of the 

 species of Cidaris common on the west coast of Lower California, Mexico, and Central America, C. thouarsii. I do not 

 think it shows a single feature by which it can be distinguished from thouarsii, it is certainly from the ancestor of that 

 species. 



Locality. — Santa Cruz quadrangle, Cal. 



Geologic horizon. — Monterey shale, middle Miocene. 



Collection. — U. S. National Museum. 



