Extinction in the Star Cluster SAI~113 and Galactic Structure in Carina
  Photometric CCD {\it UBVI}$_C$ photometry obtained for 4860 stars surrounding
the embedded southern cluster SAI~113 (Skiff~8) is used to examine the
reddening in the field and derive the distance to the cluster and nearby
van~Genderen~1. Spectroscopic color excesses for bright cluster stars,
photometric reddenings for A3 dwarfs, and dereddening of cluster stars imply
that the reddening and extinction laws match results derived for other young
clusters in Carina: E$_{U-B}/$E$_{B-V} \simeq 0.64$ and $R_V \simeq 4$. SAI~113
displays features that may be linked to a history of dynamical interactions
among member stars: possible circumstellar reddening and rapid rotation of late
B-type members, ringlike features in star density, and a compact core with most
stars distributed randomly across the field. The group van~Genderen~1 resembles
a stellar asterism, with potential members distributed randomly across the
field. Distances of $3.90 \pm0.19$ kpc and $2.49 \pm0.09$ kpc are derived for
SAI~113 and van~Genderen~1, respectively, with variable reddenings E$_{B-V}$
ranging from 0.84 to 1.29 and 0.23 to 1.28. The SRC variables CK~Car and EV~Car
may be outlying members of van~Genderen~1, thereby of use for calibrating the
period-luminosity relation for pulsating M supergiants. More importantly, the
anomalous reddening and extinction evident in Carina and nearby regions of the
Galactic plane in the fourth quadrant impact the mapping of spiral structure
from young open clusters. The distribution of spiral arms in the fourth
quadrant may be significantly different from how it is often portrayed.
