152 University of Calif ornia PnhlioaUons in Geology [Vol. 12 



Outline as seen from above suboval to eordiform ; posterior end more 

 or less truncated. Apical system very small, sunken, and central ; 

 summit placed behind apical system on the sharp ridge which extends 

 from the apical system to the periproct. Upper surface slopes grad- 

 ually to the anterior margin from the apex. Sides of the test broadly 

 rounded, except in the posterior portions, where they are nearly 

 vertical. Ambulacra petaloid. Petals of the bivium very short and 

 subelliptical to rounded in outline ; anterolateral petals broad and twice 

 the length of tlie posterior pair. Inner rows of pores of paired petals 

 diverge slightly at first, and then continue in parallel lines to the end 

 of the petal, while outer rows diverge considerably more and then 

 converge close to the inner rows. Poriferous areas wide, each being 

 as wide as the interporiferous area ; pores in both rows transversely 

 elongate. Odd anterior petal longer than the others ; both rows of 

 pores round and diverge continuously to their extremities. All 

 petals in deep sulci, the odd anterior one continuing through a deep 

 notch in the margin to the under side. Lower surface slightly convex. 

 Peristome situated well forward in a distinct transverse depression 

 liaving a prominent labrum which is produced posteriorly into a well 

 defined episternum. Periproct small, round, and situated high up on 

 the posterior truncation of the test. Peripetalous fasciole broad and 

 sinuous; lateral fasciole narrower, but distinct. Tubercles on upper 

 surface small and crowded, but become larger in the grooves of the 

 trivium and on the anterior portion of the test ; those of the under 

 side also larger and less numerous ; those of the actinal plastron 

 regularly placed in anteriorly convex rows. 



Related forms. — Schizaster lecontei Merriam is most closely related 

 to *S'. martinezcnsis Kew, from which it differs in having its apical 

 system less eccentric to the posterior of the center of the test ; and in 

 that the petals of the trivium are shorter and the petals of the bivium 

 longer. 



Geologic horizon. — Martinez group. Lower Eocene; occurring in 

 the Solen stantoni zone, Trochoscyathus zitteli zone, and Meretrix 

 dalli zone ; associated with Schizaster coreliformis Kew. 



Localities. — Type from one and one-quarter miles southeast of Muir 

 Station, on hillside northeast side of Martinez-Walnut Creek road, 

 75 feet above road, Univ. Calif, loc. 337 ; figured specimen from Muir 

 Syncline near Vine Hill Station, Contra Costa County, California. 

 Also occurs at Mount Diablo, Contra Costa County, California ; Lower 

 Lake, Lake County, California. 



