We have conducted a redshift survey of sixteen cluster candidates from the Palomar Distant Cluster Survey ( PDCS ) to determine both the density of PDCS clusters and the accuracy of the estimated redshifts presented in the PDCS catalog ( [ Postman et al . ] 1996 ) .
We find that the matched-filter redshift estimate presented in the PDCS has an error \sigma _ { z } = 0.06 in the redshift range 0.1 \leq z \leq 0.35 based on eight cluster candidates with three or more concordant galaxy redshifts .

We measure the low redshift ( 0.1 \leq z \leq 0.35 ) space density of PDCS clusters to be 31.3 ^ { +30.5 } _ { -17.1 } \times 10 ^ { -6 } h ^ { 3 } { Mpc ^ { -3 } } ( 68 % confidence limits for a Poisson distribution ) for Richness Class 1 systems .
We find a tentative space density of 10.4 ^ { +23.4 } _ { -8.4 } \times 10 ^ { -6 } h ^ { 3 } { Mpc ^ { -3 } } for Richness Class 2 clusters .
These densities compare favorably with those found for the whole of the PDCS and support the finding that the space density of clusters in the PDCS is a factor of \simeq 5 above that of clusters in the Abell catalog ( [ Abell ] 1958 ; [ Abell et al . ] 1989 ) .
These new space density measurements were derived as independently as possible from the original PDCS analysis and therefore , demonstrate the robustness of the original work .
Based on our survey , we conclude that the PDCS matched-filter algorithm is successful in detecting real clusters and in estimating their true redshifts in the redshift range we surveyed .

Keywords : galaxies : clusters : general — catalogs