112 University of California Publications in Geology [Vol. 12 



diverge strongly at first and then converge markedly about three- 

 fourths the distance to the margin, at which point they become rounded 

 and continue parallel with the inner rows to the end of the petal. 

 "Width of interporiferous areas of lateral petals over one-half the 

 breadth of the entire petal. Odd anterior petal of the same length 

 and wide open at its extremity, as in the lateral petals, but differs 

 somewhat from the others in that it is wider, due to the greater width 

 of the interporiferous area ; extends closer to the margin, and is slightly 

 less elevated than the others. Inferior surface concave to the peris- 

 tome ;, marked by distinct, straight, undivided ambulacral furrows, 

 which in some specimens pass tlirough the marginal notches on the - 

 upper surface and continue nearly to the apical system, forming a 

 slight median groove on the petal. Peristome subcentral, small, and 

 subcircular in outline. Periproct small, round, and inframarginal, 

 nearly marginal. Tubercles small, crowded, and similar over both 

 surfaces. 



Related forms. — Astrrjfl apsis whitneyi Remond differs from A. 

 tumid us Remond mainly in its much thinner margin; smaller tu- 

 bercles ; relatively less pronounced widening of the ambulacral plates 

 toward the ambitus ; flat interambulacral areas ; and in its charac- 

 teristic bell-shaped appearance. A. whitneyi seems to be very closely 

 allied to the southern form A. cejalingaensis Kew, but it is readily 

 distinguished from the latter by having a smaller tliough relatively 

 higher test ; in that the tuberculation is uniform over the surface, 

 while in A. coalingaensis the petaliferous areas support larger tu- 

 bercles ; in that tlie posterior marginal notches are comparatively 

 deeper ; and in that the periproct is situated nearer the margin. 

 Twitchell entertains doubt as to the dissimilarity between A. whitneyi 

 and A. calif ornieus Kew, but the latter may be separated by its deep, 

 broad depressed interambulacral areas, which in A. whitneyi are flat; 

 also the petals are much wider and the marginal notches are shallower. 



Geologic horizon. — Upper portion of the San Pablo group. Upper 

 Miocene, occurring with Astrodapsis tumid us Remond and A. altus 

 Kew; and "Santa Margarita" formation associated with A. tiom,idus 

 and A. ornatus Kew. 



Localities. — San Pablo Bay and Mount Diablo regions, California. 

 Type of Remond from Walnut Creek, Contra Costa County, California. 

 Figured specimens from Univ. Calif, loc. 1227. Also from San Juan 

 River district, and Quailwater Canyon, San Luis Obispo County, 

 California; Cuyama River district (U. S. Geol. Surv. Coll.) ; Salinas 

 River district (U. S. Geol. Surv. Coll.). 



