Arp 31/IC 167 made Arp's list under the category for spiral galaxies resembling the integral sign. It is the first of 6 in this category. UGC 3697 is usually referred to as the integral sign galaxy but isn't one of the 6 Arp put in his integral sign category.

To me, Arp 31 is just a wide two arm galaxy showing a short bar. It is located in western Aries about 120 million light-years from us by redshift. It was discovered on January 4, 1889 by Guillaume Bigourdan. It is classified as SAB(s)c.

The other major galaxy in the image is below Arp 31 and to the right. It is NGC 691, an SA(rs)bc galaxy. It is about 110 million light-years distant by redshift and 120 million light years by Tully-Fisher measurements so may be related to Arp 31. It was discovered by William Herschel on November 13, 1786 by William Herschel but isn't in either of the Herschel 400 programs.

Lesser galaxies are IC 1730 to the far upper right. It is listed as a, S0?? galaxy at 120 million light-years so again possibly related to the others. It was first seen by Stephane Javelle on January 17, 1896.

At the top center above Arp 31 is NGC 694 an S0? Pec starburst galaxy. It too, is 120 million light-years distant. It was discovered by Heinrich d'Arrest on December 2, 1861.

Arp's image: http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp31.jpeg

14" LX200R @ f/10, L=10x10' RGB=2x10', STL-11000XM, Paramount ME