144 University of California PuMications in Geology [Vol. 12 



Poriferous zones wide, each being about the same width as the inter- 

 poriferous area ; rows of pores do not tend to close in the odd anterior 

 petal and only to a very slight degree in the lateral ones. Pores oval 

 in shape, those of the inner rows being much more elongate than the 

 outer ones. Petals situated in deep grooves, the odd anterior one 

 continuing through a broad notch in the ambitus to the peristome on 

 the under surface. Lower surface flat, except surrounding the mouth, 

 where it is slightly depressed. Peristome transversely elongate, with 

 prominent posterior labrum. Periproct small, transversely elongate, 

 and placed high up on the posterior truncation of the test. Tuber- 

 culation prominent over the test ; consists of irregularly placed pri- 

 maries with luxmerous interspaced milliaries. The size of the tubercles 

 varies ; largest on the actinal surface, smallest near the ambitus, and 

 larger again on the abactinal side. No fascioles present. 



Related forms. — This form resembles Sehizaster lecontei Merriam 

 in general appearance, but may be separated by its more depressed 

 test ; narrower and less deeply sunken petals ; and differs also in that 

 it lacks the fascioles which characterize the genus Sehizaster. From 

 Hemiaster calif amicus Clark it differs in having much shorter petals 

 in the bivium. 



Geologic horizon. — Chico formation, Upper Cretaceous. 



Locality. — Cotypes from northern California. 



Genus HEMIASTER Desor 



HEMIASTER ALAMEDENSIS Kew, n. sp. 

 Plate 40, figures 5a, 56, 5c, 5d 



Holotype.—m. 11009 Univ. Calif. Coll. Invert. Pal. 



Size rather large. Measurements of holotype : anteroposterior di- 

 ameter 26.9 mm., transverse diameter 27.8 mm., greatest height 2.8 

 mm. Outline of test from above subcircular ; longitudinal profile sub- - 

 rectangular. Test very tumid, with the posterior extremity truncated. 

 Ui^per surface depressed and gently rounded to a low apex, which is 

 situated far back on the small ridge that extends in the odd posterior 

 interambulacral area from the apical system to the periproct. Apical 

 system i^laeed slightly to the posterior of the center of the test. 

 Petals of the bivium about seven-tenths the length of the lateral petals 



