Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
Equus (play) produced as a large-format artist's book by the Old Stile Press, with images and an afterword by the British artist Clive Hicks-Jenkins, in 2009. "Equus" was revived in San Jose, California, in March 2011 at City Lights Theater Company. This production, featuring actors Sean Gilvary as Alan Strang and Steve Lambert as Martin Dysart, received rave reviews. "The Mercury News" labeled Gilvary and Lambert as "haunting," stating Gilvary "...exposing emotions and epidermis, rides bareback in every sense. He gradually manages to make a rather unattractive young creature seem not only sympathetic but redeemable while retaining his hostility and humanity." Starkinsider