132 University of California Publications in Geology [Vol. 12 



the widtli of a marginal plate from the edge of the test. Tubercles 

 small and of uniform size on both sides of the test, except near the 

 peristome, where they become slightly larger and less crowded. The 

 spines on the upper surface are often visible, and are about one ■milli- 

 meter in length, longitudinally striated, and club-shaped, the distal 

 end being twice the size of the proximal end ; those on the under 

 surface are two to three millimeters in length, also longitudinally stri- 

 ated, but tapering to the end. 



Related forms. — Tliis species most closely resembles Calaster ore- 

 gonensis (Clark), but several constant differences exist which permit 

 C. interlineatus to be readily distinguished. The main differences 

 are : C. interlineatus has a less eccentric apical system which is con- 

 stant, lias a more nearly circvilar outline, attains a greater size, and 

 has petals more nearly elliptical and symmetrical in shape, and nearly 

 equal in length. From Scutella.- fairbanksi Arnold and S. gabhi 

 (Remond) it may easily be distinguished by its greater size, slightly 

 posteriorly eccentric apical system, and in that the periproct is sit- 

 uated farther from the margin on the upper surface. 



Discussion. — This form is without doubt the same as the poorly 

 preserved form Stimpson originally described. The type was not 

 available, but his illustration coincides in all respects with the speci- 

 mens in the collection of the University of California. In the writer's 

 opinion the specimens figured by Merriam and Twitchell do not fit 

 the original description. Stimpson 's figure shows the similar sym- 

 metrical petals, the slightly eccentric apical system, and large size, 

 all of which are distinctive for Calaster interlineatus. 



Geologic horizon. — Lower Merced series, Upper Pliocene ; in horizon 

 above that in which Calaster oregonensis var. major Kew is found. 



Locality. — Stimpson 's holotype from south of Point Lobos, near 

 San Francisco, California ; neotype, specimen no. 11353, from sea- 

 cliff's north of JMussel Rock on west side of San Francisco Peninsula, 

 San Mateo County, California. Univ. Calif, loe. 1726. 



DENDRASTER (CALASTER) OREGONENSIS (W. B. Clark) 

 Plate 33, figures 2a, 2b 



Scutella {Echinarachnius) oregonensis W. B. Clark in Dall, U. S. Geol. 



Surv. Prof. Paper, no. 59, 1909, p. 140, pi. 7, fig. 2. 

 Dendraster oregonensis. Clark and Twitchell, U. S. Geol. Surv. Mon., vol. 



54, 1915, p. 195, pi. 90, fig. 1. 



